usb: gadget: tegra-xudc: remove PEX rails

usb: gadget: tegra-xudc: remove PEX rails

Since we already moved UPHY driver from kernel to bpmp-fw, PEX rails are
no longer required in XUDC driver. Remove them here.

Bug 200251145

Change-Id: I406dbe76ed7f8ebeddd931c74af288c9ecbd92d0
Signed-off-by: Mark Kuo <mkuo@nvidia.com>
Reviewed-on: http://git-master/r/1249536
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Rohith Seelaboyina <rseelaboyina@nvidia.com>
Reviewed-by: svccoveritychecker <svccoveritychecker@nvidia.com>
Reviewed-by: WK Tsai <wtsai@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Ashutosh Jha <ajha@nvidia.com>