Convert CONFIG_SUPPORT_EMMC_RPMB to Kconfig

This converts the following to Kconfig:
   CONFIG_SUPPORT_EMMC_RPMB

This fixes a few platforms where the option was not taking effect as
intended.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/firefly-px30_defconfig b/configs/firefly-px30_defconfig
index 7207028..0a84cce 100644
--- a/configs/firefly-px30_defconfig
+++ b/configs/firefly-px30_defconfig
@@ -69,6 +69,7 @@
 CONFIG_SYS_I2C_ROCKCHIP=y
 CONFIG_MISC=y
 CONFIG_ROCKCHIP_OTP=y
+CONFIG_SUPPORT_EMMC_RPMB=y
 CONFIG_MMC_DW=y
 CONFIG_MMC_DW_ROCKCHIP=y
 CONFIG_PHY_REALTEK=y