Move setexpr to Kconfig

Another shell scripting command that has not been moved.

Moved using tools/moveconfig.py using these settings:

CMD_SETEXPR bool n y

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/configs/walnut_defconfig b/configs/walnut_defconfig
index c5b302e..f4c36b8 100644
--- a/configs/walnut_defconfig
+++ b/configs/walnut_defconfig
@@ -1,4 +1,5 @@
 CONFIG_PPC=y
 CONFIG_4xx=y
 CONFIG_TARGET_WALNUT=y
+CONFIG_CMD_SETEXPR=y
 CONFIG_REGEX=y