GRUB2 is too big as a payload in ThinkPad X201

[Iru Cai]

I tried to use GRUB2 as a payload when building coreboot for ThinkPad X201,
but it's too big to fit into the rom. The GRUB2 coreboot image without
modules is 2.8M and >800K after compressing, it's still too big.

I think FILO and u-boot are good alternatives but not so user-friendly and
documented as GRUB2, so it's time to find a way to slim down GRUB2 as a
coreboot payload.