nds32: Fix gcc 8.0 compiler option incompatible.

When the kernel configs of ftrace and frame pointer options are
choosed, the compiler option of kernel will incompatible.
	Error message:
		nds32le-linux-gcc: error: -pg and -fomit-frame-pointer are incompatible

Signed-off-by: Nickhu <nickhu@andestech.com>
Signed-off-by: Zong Li <zong@andestech.com>
Acked-by: Greentime Hu <greentime@andestech.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>