Revert "clk: gxbb: expose CLKID_MMC_PCLK"

This reverts commit e16fb2e635.

Updated documentation from the chip vendor reveals that this clock is
not required for correct operation of the MMC controller. As such, do
not expose it to DT.

Signed-off-by: Michael Turquette <mturquette@baylibre.com>

include/dt-bindings/clock/gxbb-clkc.h

@@ -8,6 +8,5 @@
 #define CLKID_CPUCLK		1
 #define CLKID_CLK81		12
 #define CLKID_ETH		36
-#define CLKID_MMC_PCLK		66
 
 #endif /* __GXBB_CLKC_H */