treewide: Migrate CONFIG_BOARD_EARLY_INIT_R to Kconfig

Migrate the CONFIG_BOARD_EARLY_INIT_R option to Kconfig.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/configs/MPC8536DS_36BIT_defconfig b/configs/MPC8536DS_36BIT_defconfig
index cdef677..953a923 100644
--- a/configs/MPC8536DS_36BIT_defconfig
+++ b/configs/MPC8536DS_36BIT_defconfig
@@ -9,6 +9,7 @@
 CONFIG_BOOTDELAY=10
 # CONFIG_CONSOLE_MUX is not set
 CONFIG_BOARD_EARLY_INIT_F=y
+CONFIG_BOARD_EARLY_INIT_R=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_IMLS=y
 CONFIG_CMD_I2C=y