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/octeontx_83xx_defconfig b/configs/octeontx_83xx_defconfig
index 4cfd4ea..2675934 100644
--- a/configs/octeontx_83xx_defconfig
+++ b/configs/octeontx_83xx_defconfig
@@ -72,6 +72,7 @@
 CONFIG_AHCI_PCI=y
 CONFIG_DM_I2C=y
 CONFIG_MISC=y
+CONFIG_SUPPORT_EMMC_RPMB=y
 CONFIG_SUPPORT_EMMC_BOOT=y
 CONFIG_MMC_OCTEONTX=y
 CONFIG_MTD=y