da8xx: Add the missing pinmux for da830 to the gpio driver

The pinmux was generated from linux/arch/arm/mach-davinci/da830.c as of
kernel version 3.7.5. If the driver is used for the da850, then SoC
variant must be specified by CONFIG_SOC_DA850.

Signed-off-by: Tomas Novotny <tomas@novotny.cz>
Cc: Tom Rini <trini@ti.com>