usb: dwc3: Enable PHY deep low power mode in L1 suspend

Currently controller is enabling only shallow low power mode during
L1 suspend in host mode. Power savings can be improved by allowing
deep low power mode allowing PLL to be turned OFF. Configuring
the GUCTL1 register to enable this feature.

Change-Id: Iea6cfa2c9085a01f45a9f0d633c80368ad085806
Signed-off-by: Elson Roy Serrao <eserrao@codeaurora.org>