usb: dwc2: gadget: Accept LPM token when TxFIFO is not empty

Set GLPMCFG_LPM_ACCEPT_CTRL_ISOC bit in GLPMCFG register
to accept LPM token during ISOC transfers when TxFIFO is
not empty.

- Added two definitions.
  	#define GLPMCFG_LPM_ACCEPT_CTRL_CONTROL        BIT(21)
  	#define GLPMCFG_LPM_ACCEPT_CTRL_ISOC   BIT(22)
  This patch uses GLPMCFG_LPM_ACCEPT_CTRL_ISOC.
  GLPMCFG_LPM_ACCEPT_CTRL_CONTROL is defined for further use.

- Added setting GLPMCFG_LPM_ACCEPT_CTRL_ISOC bit in GLPMCFG
  register in dwc2_gadget_init_lpm function.

Signed-off-by: Artur Petrosyan <arturp@synopsys.com>
Signed-off-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>