arm/dt: msm8974: spi_qsd: Add support for clock path voting

Voting for the entire clock path (using the bus-scaling driver)
requires information about the master endpoint number. A second
new field signals the driver if vote should follow the runtime-pm
state or the application processor power state. These values
are configured in the device tree. In addition, the device-tree
binding document is updated to reflect the new fields.

Change-Id: Ie97cfd209c77fbee01a0ea4f44fa1a34377af519
Signed-off-by: Gilad Avidov <gavidov@codeaurora.org>