Update bootrom code with the latest hardware.inc

[Rangi42]

Bootrom code is updated to use new hardware.inc constants, as well as for consistent formatting.

The ROMs are unchanged:

$ sha1sum build/bin/BootROMs/*.bin
4ed1d95c9c682a78698f235ce9e9bb3b62bccf9f  build/bin/BootROMs/agb_boot.bin
822728fbe1d637528c57659ad86e0bf5da666677  build/bin/BootROMs/cgb0_boot.bin
113903775a9d34b798c2f8076672da6626815a91  build/bin/BootROMs/cgb_boot.bin
1db57a1e8b6e4096f811587f9eab0c6675fd9755  build/bin/BootROMs/dmg_boot.bin
9817bdae9335a3accb584f77c165dc5726555d1f  build/bin/BootROMs/mgb_boot.bin
f282b3aaf98f8423dab7d77f1aa0192be630f2fb  build/bin/BootROMs/sgb2_boot.bin
369e6eb5e0c975eaa52a4a3f6ee07b2a3c3c16de  build/bin/BootROMs/sgb_boot.bin

These should still build with RGBDS 0.5.0 through 0.8.0 (master). Compatibility notes:

• 0.8.0 will deprecate -i, requiring -I, so we just use the long --include option.
• Using halt without an implicit nop after it requires version-specific flags. RGBASM 0.5.0 and 0.6.0 needed -h to disable it; 0.7.0 does so by default. (0.7.0 lets you opt in with -H, but 0.8.0 will remove that entirely.)

[LIJI32]

Great work! I've been wanting to eventually clean SameBoot up and use hardware.inc more "fully", but I never had the chance, and you probably did a far better job than I would. I do have a few comments though:

1. The Makefile has a few unnecessary whitespace change, can you rebase them away so they don't screw git blame up?
2. I'd have a Make variable for RGBASM flags instead of having them inline calculated on build. It looks a bit cleaner and is slightly faster.
3. ld hl, (BOOTUP_A_MGB << 8) | $B0 and co. could use the lb macro.
4. CgbFlag, SgbFlag, RomSize and RamSize should be CGBFlag, SGBFlag, ROMSize and RAMSize, respectively.