blkcache: Extend blkcache_init to cover CONFIG_NEEDS_MANUAL_RELOC

Extend manual relocation of block_cache list pointers to all platforms that
enable CONFIG_NEEDS_MANUAL_RELOC. Remove m68k-specific checks and provide a
single implementation that adds gd->reloc_off to the pre-relocation
pointers.

Acked-by: Angelo Dureghello <angelo.dureghello@timesys.com>
Tested-by: Angelo Dureghello <angelo.dureghello@timesys.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Eric Nelson <eric@nelint.com>
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>