Additional registers and fields for USB host support

[nilclass]

Related to https://github.com/rp-rs/rp-hal/pull/660

Changes:

• Adds single EPX_CONTROL register, as a copy of the EP_CONTROL registers (thanks to @ithinuel for figuring out how to express this!)
• Adds HOST_POLL_INTERVAL field to the EP_CONTROL registers. This field may only be used in host mode. It overlaps with the existing INTERRUPT_ON_STALL / INTERRUPT_ON_NAK fields, which must not be used in host mode.
• Collect ADDR_ENDP1 to ADDR_ENDP15 into an array named HOST_ADDR_ENDP. These registers are used to set up interrupt pipes. They aren't used in device mode. The ADDR_ENDP register (without a number) which is also used by the device mode, is not part of the array.

[nilclass]

Does the HOST_POLL_INTERVAL field also apply to epx_control ?

It doesn't seem to be added. If that's expected, I'm happy with the PR.

It's not needed for epx_control. Technically it's also not needed for the "EP*_OUT_CONTROL" registers (which are unused in host mode), but the IN and OUT variants must have the same fields to be turned into an array.

[nilclass]

I've added one more change just now, regarding ADDR_ENDP1-15 (description updated above).

[nilclass]

I left as suggestion to enhance readability of the yaml file (and avoid error prone repetitions).

Nice, applied, that's much better!