msm: pcie: aggregate PCIe rate change clock vote

PCIe rate change clock is shared among all PCIe ports. Based on
use case, each PCIe will vote for either 19.2MHz or 100HMz. Only
the last vote counts. Therefore, add support to aggregate all
votes and set the clock rate to meet all PCIe requirements.

Change-Id: Iaf6aa0ef667e4f89ce8653ed6958c76367d2dd2a
Signed-off-by: Tony Truong <truong@codeaurora.org>