spi: zynqmp: Add pm runtime support

This patch adds runtime pm functions.

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Signed-off-by: Naga Sureshkumar Relli <nagasure@xilinx.com>
Signed-off-by: Mark Brown <broonie@kernel.org>