spi: spi-geni-qcom: Use autosuspend for runtime PM

The driver uses runtime framework to manage resources which are enabled
and disabled before each SPI message. These have an associated time
overhead with them.
If a client uses lots of smaller SPI messages, then unfortunately the
resource overhead will show up in each message.
The change also takes into account the fact that if an Serial Engine(SE)
is shared then vote the GPIOs off immediately since that resource is not
aggregated between the two Execution Enviroments (EE) sharing this SE.
The clocks can be turned off after the auto-suspend timer expires as those
resources are aggregated between the two EEs.

Change-Id: Id1350335e0b29d59f043d40d290f6b74af1edcc8
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>