drivers: usb_c: numaker: update UTCPD.VBSCALE register field

This follows update of UTCPD.VBSCALE register field. It supports:
- "divide-20": External VBUS voltage divider circuit should be 1/20
               for EPR application. The divided voltage compares with
               200mV to set or clean VBUS Present bit.
- "divide-10": External VBUS voltage divider circuit should be 1/10
               for SPR application. The divided voltage compares with
               400mV to set or clean VBUS Present bit.

Signed-off-by: Chun-Chieh Li <ccli8@nuvoton.com>