drivers: display: mb_display: Add include of toolchain.h for __printf_like

When we build with newlib __printf_like is already defined so we run
into issues.  We should include toolchain.h to properly handle this.

Change-Id: Ia961a9f1d3f7bf965e4115eb93a7ba6a62220905
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>