usb: dwc3: Allocate fixed h/w eps for GSI endpoints

Adds support to allocate specific hardware EPs to
GSI enabled endpoints. Creates EP list with names
"gsi-epin" for IN and "gsi-epout" for OUT EPs that
are intended for use by the GSI function driver.
The EPs are reserved from the end of the EP list.

CRs-Fixed: 946385

Change-Id: I70ebce8c2717baaea38f7b6235976d8a522eb9fd
Signed-off-by: Devdutt Patnaik <dpatnaik@codeaurora.org>