usb: dwc3: debugfs: Add suppot for Enabling L1 in HS through debugfs

Currently the kernel implementation disables L1 in HS since
there are target which does not support gadget L1.
However, implementing this leads to Ch9 compliance
failures.
Therefore implementing a debugfs parameter through which
this can be controlled, when testing for compliance it can
be set to true and carry out the tests.

Change-Id: I9cf9c49737b18ca889fcc1dbe8232a7bb999f35c
Signed-off-by: Udipto Goswami <ugoswami@codeaurora.org>