This streamlines the boot code a bit and reduces target specific
boilerplate. The clock init hack used by the bootloader has been
"standardized" and works for the main Rockbox binary now, so you
can boot rockbox.bin over USB without special hacks.
Change-Id: I7c1fac37df5a45873583ce6818eaedb9f71a782b
SPL and UCL-compressed bootloader are now packed into one output,
bootloader.m3k, eliminating the separate SPL build phase.
The Rockbox bootloader now has a recovery menu, accessible by
holding VOL+ when booting, that lets you back up, restore, and
update the bootloader from the device.
Change-Id: I642c6e5fb83587a013ab2fbfd1adab439561ced2
