clk: msm: Add virtual clock frontend driver

It is virtual clock frontend driver which communicates
with host backend clock service/driver over HABMM. It
only supports msm8996 virtual platform currently.

Change-Id: Icfee28c301fa4a583b45e5d364432535643eb9b7
Signed-off-by: Zhiqiang Tu <ztu@codeaurora.org>