mmc: tmio: add references to bit defines in the header

When defining bits, make sure we always have a reference to the register
they belong to. For now, renaming all bits properly seems too intrusive,
so at least make sure we have proper documentation.
Signed-off-by: NWolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/tmio_mmc.h

@@ -81,9 +81,11 @@
 #define TMIO_STAT_CMD_BUSY      BIT(30)
 #define TMIO_STAT_ILL_ACCESS    BIT(31)
 
+/* Definitions for values the CTL_SD_CARD_CLK_CTL register can take */
 #define	CLK_CTL_DIV_MASK	0xff
 #define	CLK_CTL_SCLKEN		BIT(8)
 
+/* Definitions for values the CTL_SD_MEM_CARD_OPT register can take */
 #define CARD_OPT_WIDTH8		BIT(13)
 #define CARD_OPT_WIDTH		BIT(15)