efi_loader: select BLK not depends on BLK

efi_loader: select BLK not depends on BLK

The BLK symbol is used both for "we have a block device subsystem
enabled" and "we need to utilize the block device library functions". In
the case of efi_loader, it is the case of "we need to utilize the block
device library", so select rather than depends on it. In turn, also
disable EFI_LOADER on platforms which did not have it on previously due
to a lack of block devices. They can enable it themselves if desired.

Acked-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>