ARM: dts: msm: Add dummy clock controllers for sdxpoorwills

Define dummy clock controllers for GCC and CPU clocks
for sdxpoorwills. Add the list of supported clock bindings
to allow clients to use the correct clock names.

Change-Id: Ief779965e4a266f8abd4d4568538b83fdf8e1501
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>