pinmux: Add support for ARM V2M Beetle Initialization

This patch adds the support for the board pinmux initialization on
ARM V2M Beetle.

The GPIO controllers 2 and 3 are reserved and therefore neither exposed
nor configured by this driver.

Jira: ZEP-1245
Change-Id: Id5499c5dd887c319730408eeb30f02eeed1c3699
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@linaro.org>
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>