arm/dt: msm8974: qup_i2c: Add support for clock path voting

Voting for the entire clock path (using the bus-scaling driver)
requires information about the master endpoint number. This
number is configured to the driver via the device tree.
In addition, the device-tree binding document is updated
to reflect the new fields.

CRs-Fixed: 483873
Change-Id: Ic3a0199d9eb661c2614a7d0ae21b0cebdc189bf3
Signed-off-by: Gilad Avidov <gavidov@codeaurora.org>