include: espi.h: Update OCB virtual wires mappings

update espi_vwire_signal enum to refer all platform specific
usage virtual wires to ESPI_VWIRE_SIGNAL_SLV_GPIO_x
Virtual wires used for USB-C port over current (OCB)
have been defined as macros mapped to the corresponding
espi_vwire_signal enum

Signed-off-by: Jay Vasanth <jay.vasanth@microchip.com>