Create minimal driver VMs

[boinkaput]

This PR creates minimal linux and initramfs images for the virtio and virtio-snd examples.

[Ivan-Velickovic]

Could you summarise what you modified in the Linux kernels? What configuration options did you disable?

[boinkaput]

@Ivan-Velickovic here's a summary of the updated config:

• Selected the minimum number of CPUs (which is 2)
• Removed support for high res timers
• Selected "no forced preemption" model for the kernel. As per the definition: it leads to better throughput and is better suited for servers.
• Disabled NUMA support
• Enabled support for initramfs and only supports gzipped images
• Enabled config expert and selected the following options:
  • CONFIG_BASE_FULL: full sized kernel data structures
  • CONFIG_FUTEX: required by glibc applications
  • CONFIG_TIMERFD: required by the uio sound driver
  • CONFIG_SHMEM: used by tmpfs
  • everything else (like cgroups, namespaces, etc) has been disabled
• For platform selection, I chose CONFIG_ARCH_MESON (not sure if we require other platforms atm, as we are only supporting qemu and odroidc4)
• Disabled virtualization
• Enabled module support: used by the sound and block drivers to add additional functionality on top of the base kernel through the use of modules
• Disabled all power management options to prevent any policy conflicts with microkit.
• Only has support for elf binaries.
• Enabled free page reporting: will be useful if we decide to implement memory ballooning or any other kind of cooperative memory management.
• Disabled all networking support
• Disabled all filesystems, except for tmpfs and sysfs
• Disabled all device driver except for the ones that were automatically enabled by selecting CONFIG_ARCH_MESON platform support and PCI support.
• Disabled crypographic API, library routines and any other debug options
• /dev/mem will still be present because it is required by the sound driver.
• Enabled the block layer for virtio block (no other options are enabled in its submenu).
• Enabled support for sound devices, ALSA and USB support (for audio devices that require USB). Most of these are enabled as modules, but some of them only have a yes/no option.