spi: omap2-mcspi: Add calls for pinctrl state select

This adds calls to pinctrl subsystem in order to switch pin states
on suspend/resume if you provide a "sleep" state in DT.

If no "sleep" state is provided in DT, these calls turn
to NOPs.

Signed-off-by: Pascal Huerst <pascal.huerst@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>