uboot-imx

block: Have BLOCK_CACHE default to y in some cases

When dealing with filesystems that come from block devices we can get a
noticeable performance gain in some use cases from having the block
cache enabled.  The code paths are valid in other cases when we have BLK
set and may provide wins in raw reads in some use cases, so have this be
default when BLK is enabled.

Signed-off-by: Tom Rini <trini@konsulko.com>