tests: drivers: disk: Update outdated prj.conf

The proj.conf for these two tests was unconditionally
selecting SDMMC disk drivers which is incorrect now that
there are DT macros that are used to select these Kconfigs.

This also allows the test to be used for other disk protocols
such as MMC, as before this change, SDMMC would still be selected
and cause errors at runtime.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>