mmc: sdhci-pic32: allow driver to be compiled with COMPILE_TEST

mmc: sdhci-pic32: allow driver to be compiled with COMPILE_TEST

This driver currently only supports builds against a PIC32 target. Now
that commit d6618d277c1a ("mmc: sdhci-pic32: update include to use
pic32.h from platform_data") is merged, it's possible to compile this
driver on other architectures.

To avoid future breakage of this driver in the future, let's update the
Kconfig so that it can be built with COMPILE_TEST enabled on all
architectures.

Signed-off-by: Brian Masney <bmasney@redhat.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>