gpio/omap: ensure gpio context is initialised

Commit a2797be (gpio/omap: force restore if context loss is not
detectable) broke gpio support for OMAP when booting with device-tree
because a restore of the gpio context being performed without ever
initialising the gpio context. In other words, the context restored was
bad.

This problem could also occur in the non device-tree case, however, it
is much less likely because when booting without device-tree we can
detect context loss via a platform specific API and so context restore
is performed less often.

Nevertheless we should ensure that the gpio context is initialised
during the probe for gpio banks that could lose their state regardless
of whether we are booting with device-tree or not.

Reported-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Merge branch 'omap-dma-for-v3.10' into omap-daily-testing
Merge branch 'omap-dmtimer-for-v3.10' into omap-daily-testing
Merge branch 'omap-dt-for-v3.10-take2' into omap-daily-testing
Merge branch 'omap-gpio-for-v3.10' into omap-daily-testing
Merge branch 'omap-gpmc-for-v3.10-take2' into omap-daily-testing
Merge branch 'omap-timer-for-v3.10' into omap-daily-testing
Merge branch 'omap-fixes-for-v3.10' into omap-daily-testing