configs/minnowboard_max-graphical: wchar/grub2 fix

minnowboard_max-graphical_defconfig has the line "BR_TARGET_GRUB2=y",
but this currently has no effect because BR_TARGET_GRUB2 cannot be
selected without BR2_TOOLCHAIN_BUILDROOT_WCHAR=y, which is not set by
default.

The minnowboard max defconfig was updated to fix this problem, but the
graphical variant was not updated alongside it.

Signed-off-by: Nicholas Sielicki <sielicki@yandex.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
(cherry picked from commit f27c1b82cd13a4bdbf6833110f55d4203a375066)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/minnowboard_max-graphical_defconfig

@@ -6,6 +6,8 @@ BR2_x86_atom=y
 BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_4_12=y
 BR2_TOOLCHAIN_BUILDROOT_LOCALE=y
 BR2_TOOLCHAIN_BUILDROOT_CXX=y
+# needed for TARGET_GRUB2
+BR2_TOOLCHAIN_BUILDROOT_WCHAR=y
 
 # System configuration
 BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV=y