msm: ep_pcie: Set clock power management bit for EP

According to PCIe spec, PCIE_CAP_CLOCK_POWER_MAN bit in
LINK_CAPABILITIES_REG register should be set for EP. But it is seen as
cleared after core reset. In the current driver this bit is being set
but it is not taking effect. Enabling CLK_PM_EN in PCIE_ELBI_SYS_CTRL
register, so that PCIE_CAP_CLOCK_POWER_MAN is set.

Change-Id: I16654d5a477fa8eeaad61d6ec1dd32757627e2f9
Signed-off-by: Sai Chaitanya Kaveti <quic_skaveti@quicinc.com>