Convert CONFIG_MISC_INIT_R to Kconfig

This converts the following to Kconfig:
   CONFIG_MISC_INIT_R

Signed-off-by: Adam Ford <aford173@gmail.com>
[trini: Update the defaults logic slightly]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/sama5d2_xplained_mmc_defconfig b/configs/sama5d2_xplained_mmc_defconfig
index 848f14c..6f2efe7 100644
--- a/configs/sama5d2_xplained_mmc_defconfig
+++ b/configs/sama5d2_xplained_mmc_defconfig
@@ -25,6 +25,7 @@
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 earlyprintk root=/dev/mmcblk1p2 rw rootwait"
+CONFIG_MISC_INIT_R=y
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SPL_SEPARATE_BSS=y
 CONFIG_HUSH_PARSER=y