staging: dwc2: validate the value for phy_utmi_width

The HWCFG4 register stores the supported utmi width values (8, 16 or
both). This commit reads that value and validates the configured value
against that.

If no (valid) value is given, the parameter defaulted to 8 bits
previously.  However, the documentation for dwc2_core_params_struct
suggests that the default should have been 16. Also, the pci bindings
explicitely set the value to 16, so this commit changes the default to
16 bits (if supported, 8 bits otherwise).

With the default changed, the value set in pci.c is changed to -1 to
make it autodetected as well.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>
Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>