msm: pcie: Add the regulator node for PCI-E client

It is better to control the gpio90 with regulator-fixed
framework, which can offer the VDD for PCI-E client. We
make it more modularized in this way.Also it is more suitable
for adjusting the powering position to the beginning of
enumerating, which can save more powering at RBSC.

Change-Id: Ie49faa663bb99ddf8d40b0810725508cd44c77e7
Signed-off-by: xiaolin <xiaolin@codeaurora.org>