usb: dwc2: Rename CONFIG_DWC2_UTMI_PHY_WIDTH to CONFIG_DWC2_UTMI_WIDTH

For some reason from day one we used to have both CONFIG_DWC2_UTMI_WIDTH
mentioned in dwc2.h and in scripts/config_whitelist.txt but never really used
and CONFIG_DWC2_UTMI_PHY_WIDTH used in real code in dwc2.c (but never
defined).

Moreover even though CONFIG_DWC2_UTMI_WIDTH might be either 8 or 16
depending on hardware (and the same is said in a comment for it in
dwc2.h) but then 8 is hardcoded in the header leaving no ability to
override this value in board's configuration.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Marek Vasut <marex@denx.de>