ARM: uniphier: remove BLK select

This is a user configurable option, but "select BLK" forces users to
enable it.

Even with this commit, BLK is still enabled by "default y if DM_MMC"
for UniPhier SoCs; the difference is users can disable it if they
do not need it.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>