ARM: rmobile: Convert CONFIG_ARCH_RMOBILE_BOARD_STRING to Kconfig

Convert the symbol to Kconfig, no functional change.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/configs/armadillo-800eva_defconfig b/configs/armadillo-800eva_defconfig
index 2c212e2..753077b 100644
--- a/configs/armadillo-800eva_defconfig
+++ b/configs/armadillo-800eva_defconfig
@@ -2,6 +2,7 @@
 # CONFIG_SYS_THUMB_BUILD is not set
 CONFIG_ARCH_RMOBILE=y
 CONFIG_SYS_TEXT_BASE=0xE80C0000
+CONFIG_ARCH_RMOBILE_BOARD_STRING="Armadillo-800EVA Board"
 CONFIG_R8A7740=y
 CONFIG_TARGET_ARMADILLO_800EVA=y
 CONFIG_BOOTDELAY=3