rockchip: rk3188: enable TPL_LIBGENERIC for generic memset

Commit c67c8c60 ("board_init.c: Always use memset()") dropped the naive
memset alternative from board_init_f_init_reserve.
So activate CONFIG_TPL_LIBGENERIC for that common memset implementation.
We cannot use the ARCH-specific memset, as that would incur 200bytes of
additional TPL size, space we do not have.
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>

arch/arm/mach-rockchip/rk3188/Kconfig

@@ -18,6 +18,9 @@ config SPL_SERIAL_SUPPORT
 config TPL_LIBCOMMON_SUPPORT
 	default y
 
+config TPL_LIBGENERIC_SUPPORT
+	default y
+
 config TPL_SERIAL_SUPPORT
 	default y