ARM: dts: msm: Use dummy provider for CPU clock on rumi 8994

RUMI does not model clock details, and thus it's necessary to use a
dummy provider for CPU clocks. Otherwise, CPUFreq will fail due to
missing CPU clocks.

Change-Id: Ib01ab070b878eef40e5c7cc80086ef08710718c0
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>