powerpc/microwatt: Add LiteX MMC driver

Enable the LiteX MMC device and it's dependency the common clock
framework.
Signed-off-by: Joel Stanley <joel@jms.id.au>
Acked-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220804015708.5928-1-joel@jms.id.au

arch/powerpc/configs/microwatt_defconfig

@@ -75,7 +75,12 @@ CONFIG_SPI_BITBANG=y
 CONFIG_SPI_SPIDEV=y
 # CONFIG_HWMON is not set
 # CONFIG_USB_SUPPORT is not set
+CONFIG_MMC=y
+# CONFIG_PWRSEQ_EMMC is not set
+# CONFIG_PWRSEQ_SIMPLE is not set
+CONFIG_MMC_LITEX=y
 # CONFIG_VIRTIO_MENU is not set
+CONFIG_COMMON_CLK=y
 # CONFIG_IOMMU_SUPPORT is not set
 # CONFIG_NVMEM is not set
 CONFIG_EXT4_FS=y