drivers: usb_dc_sam: Use mode-specific interrupt register fields

The new Atmel DFP USBHS component headers provide mode-specific
interrupt register field definitions that replace the generic
definitions (e.g. `USBHS_DEVEPTISR_RXSTPI` for a control endpoint is
now `USBHS_DEVEPTISR_CTRL_RXSTPI`).

This commit updates the Zephyr SAM USBHS driver to use the new
mode-specific interrupt register field definitions.

In addition, it maps the generic definitions to the mode-specific
definitions, as the revision A variant headers (e.g. same70a) in the
latest DFPs, at the time of writing, still provide only the generic
definitions.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>