usb: dwc3: meson-g12a: fix suspend resume regulator unbalanced disables

usb: dwc3: meson-g12a: fix suspend resume regulator unbalanced disables

When going in suspend, in Device mode, then resuming back leads
to the following:

unbalanced disables for USB_PWR_EN
WARNING: CPU: 0 PID: 163 at ../drivers/regulator/core.c:2590 _regulator_disable+0x104/0x180
Hardware name: Amlogic Meson G12A U200 Development Board (DT)
[...]
pc : _regulator_disable+0x104/0x180
lr : _regulator_disable+0x104/0x180
[...]
Call trace:
 _regulator_disable+0x104/0x180
 regulator_disable+0x40/0x78
 dwc3_meson_g12a_otg_mode_set+0x84/0xb0
 dwc3_meson_g12a_irq_thread+0x58/0xb8
 irq_thread_fn+0x28/0x80
 irq_thread+0x118/0x1b8
 kthread+0xf4/0x120
 ret_from_fork+0x10/0x18

This disables the regulator if enabled on suspend, and the reverse on
resume.

Fixes: c99993376f72 ("usb: dwc3: Add Amlogic G12A DWC3 glue")
Tested-by: Kevin Hilman <khilman@baylibre.com>
Reported-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>