firmware: add microcode package for Intel

firmware: add microcode package for Intel

Compiling the Intel microcode package results in a
microcode.bin and a microcode-64.bin. As we can
decide based on the subtarget which should be used,
we'll only split the required .bin file with
iucode-tool.

x64 will get the intel-microcode-64.bin
All other variants will get intel-microcode.bin

The microcodes will be updated from preinit via a common
script - that's the earliest place where we can do it.

Signed-off-by: Zoltan HERPAI <wigyori@uid0.hu>