msm: pcie: make AUX and core clock to be asynchronous

AUX clock and core clock should be asynchronous unless L1ss
is supported and aux_clk_sync is not defined in devicetree.

Change-Id: Id448674c1c157e222bb62d6a680f9acef157d8ee
Signed-off-by: Tony Truong <truong@codeaurora.org>