ANDROID: GKI: usb: core: Add helper function to return controller id

Function provides controller id used by a remote entity
to identify which usb controller to program to initiate
data transfer.

Test: build
Bug: 151977651
Change-Id: Ied396f34496104c139a7910ee86844c124e6803f
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
(cherry picked from commit f906c280)
[hridya: EXPORT_SYMBOL -> EXPORT_SYMBOL_GPL]
Signed-off-by: Hridya Valsaraju <hridya@google.com>