davinci: da8xx/omap-l1: fix build error when CONFIG_DAVINCI_MUX is undefined

The da8xx/omap-l1 boards refuse to build when CONFIG_DAVINCI_MUX is undefined
because arch/arm/mach-davinci/mux.c:da8xx_pinmux_setup() is not defined.

This patch fixes this issue. This is build tested with davinci_all_defconfig
and da8xx_omapl_defconfig and boot tested on DA830 EVM.
Reported-by: Shanmuga Sundaram Mahendran <shanmuga@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>

arch/arm/mach-davinci/include/mach/da8xx.h

@@ -144,6 +144,10 @@ extern const short da850_mmcsd0_pins[];
 extern const short da850_nand_pins[];
 extern const short da850_nor_pins[];
 
+#ifdef CONFIG_DAVINCI_MUX
 int da8xx_pinmux_setup(const short pins[]);
+#else
+static inline int da8xx_pinmux_setup(const short pins[]) { return 0; }
+#endif
 
 #endif /* __ASM_ARCH_DAVINCI_DA8XX_H */