meta-lxatac-bsp: linux-lxatac: upgrade to 6.8 and add Gen 3 support

[hnez]

meta-lxatac-bsp: linux-lxatac: upgrade to 6.8

umpf tag is now: 6.8/customers/lxa/lxatac/20240328-1 The tag includes the following topic branches:

• v6.8/topic/reproducible-build
• v6.7/topic/net-ksz-switch
• v6.8/topic/mmc-fix
• v6.8/topic/mipi-dbi-memory-leak
• v6.8/customers/lxa/lxatac

This means we got rid of two topic branches, thanks to @ukleinek's mainlining efforts, but gained two new topic branches:

• v6.7/topic/net-ksz-switch

  Fixes RGMII drive strength configuration on our ethernet switch, that we need for EMI reasons. This means we were able to drop our previous hack that sets the drive strength.

• v6.8/topic/mmc-fix

  Fixes a regression in the MMC subsystem.

• v6.8/topic/mipi-dbi-memory-leak

  Reverts changes to the DRM subsystem that cause a memory leak on our system.

The linux-lxatac.bb has also changed a bit because umpf has started setting the PV variable series.inc in a way that collided with our previous definition.

This PR also adds support for the newest generation of LXA TACs in the form of the STM32MP153C based Generation 3.

TODO before merging:

• [x] Wait for linux 6.8 to be released and update the tarball URL and checksum
• [x] Fix a memory leak in the DRM subsystem:

  
  root@lxatac-00005:~# cat /sys/kernel/debug/kmemleak
  …
  unreferenced object 0xcb70d800 (size 1024):
    comm "kworker/1:3", pid 99, jiffies 4294900635
    hex dump (first 32 bytes):
      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    backtrace (crc 3d570562):
      [<cc328c0f>] kmemleak_alloc+0x70/0x9c
      [<b7c379de>] __kmalloc_node_track_caller+0x284/0x3dc
      [<f81aa831>] krealloc+0x54/0xa4
      [<a0b72ad8>] drm_fb_xfrm+0x298/0x308
      [<8e58b5f0>] drm_fb_xrgb8888_to_rgb565+0x58/0x64
      [<28d2288d>] mipi_dbi_buf_copy+0x10c/0x17c
      [<e90b5b20>] mipi_dbi_fb_dirty+0x9c/0x184
      [<9ba8d022>] mipi_dbi_pipe_update+0xa8/0xe8
      [<43a5f8d1>] drm_atomic_helper_commit_planes+0xfc/0x394
      [<18eccf29>] drm_atomic_helper_commit_tail+0x48/0x8c
      [<6c030577>] commit_tail+0x15c/0x180
      [<59e8f9d0>] drm_atomic_helper_commit+0x134/0x158
      [<9f9413e9>] drm_atomic_commit+0xac/0xe0
      [<acfcf0cb>] drm_atomic_helper_dirtyfb+0x174/0x24c
      [<9b629b71>] drm_fbdev_generic_helper_fb_dirty+0x220/0x2c0
      [<711c79fa>] drm_fb_helper_damage_work+0x84/0x180
  …

[hnez]

Hi @a3f, would you be interested in reviewing this PR? We would like to release a new meta-lxatac / tacos stable release containing LXA TAC hardware generation 3 support some time this week to get ready to ship devices, so it would be great to get this reviewed sooner than later.

The current solution (git revert the changes that introduced it) to the memory leak problems in the display driver is admittedly not great, but a proper fix requires a task and planned time to work on it - not quite what we have in mind timeline-wise.