x86: fix CONFIG_X86_RESERVE_LOW_64K=y

The bad_bios_dmi_table() quirk never triggered because we do DMI setup
too late. Move it a bit earlier.

Also change the CONFIG_X86_RESERVE_LOW_64K quirk to operate on the e820
table directly instead of messing with early reservations - this handles
overlaps (which do occur in this low range of RAM) more gracefully.

Signed-off-by: Ingo Molnar <mingo@elte.hu>