Add ring buffer to enable tracing of significant events of eMMC in both CQ and Legacy mode for debug purpose. CONFIG_MMC_RING_BUFFER should be enabled to use ring buffer logging. Change-Id: Iceb404d77fca19e133c319bc66ec15b2d77c7c54 Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>