Move efi_read_from_pa, efi_set_systbl and efi_bi_loadsmap into efi.c
Move prototype for populate_avail_from_efi as well, though that arrived
previously.

Move efi memory map variables into efi.c.

Add efi_read_from_sysfs, but if 0 it out. We'll want to use it if we can
get the proposed /sys/firmware/efi/memmap data published in the same
format and the code works, it's just that the current
/sys/firmware/efi/runtime-memmap isn't complete enough to use.

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