Convert CONFIG_BOUNCE_BUFFER to Kconfig

This converts the following to Kconfig:
   CONFIG_BOUNCE_BUFFER
Signed-off-by: NTom Rini <trini@konsulko.com>

include/configs/px30_common.h

@@ -32,9 +32,6 @@
 
 #define CONFIG_SYS_BOOTM_LEN	(64 << 20)	/* 64M */
 
-/* MMC/SD IP block */
-//#define CONFIG_BOUNCE_BUFFER
-
 #define CONFIG_SYS_SDRAM_BASE		0
 #define SDRAM_MAX_SIZE			0xff000000
 #define SDRAM_BANK_SIZE			(2UL << 30)