mmc: sdhci-brcmstb: Allow building with COMPILE_TEST

mmc: sdhci-brcmstb: Allow building with COMPILE_TEST

This driver is pretty simple, and it can be useful to build it (for
validation purposes) without BMIPS or ARCH_BRCMSTB.

It technically depends on CONFIG_OF to do anything useful at runtime,
but it still works out OK for compile-testing using the !OF stubs.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20221024181759.2355583-1-briannorris@chromium.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>