MIPS: fw: Record prom memory

boot_mem_map is nolonger exist so we need to maintain a list
of prom memory by ourselves.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: yasha.che3@gmail.com
Cc: aurelien@aurel32.net
Cc: sfr@canb.auug.org.au
Cc: fancer.lancer@gmail.com
Cc: matt.redfearn@mips.com
Cc: chenhc@lemote.com