Add support for BCM4378 as implemented on the Apple M1. This chip seems

Add support for BCM4378 as implemented on the Apple M1.  This chip seems
to use a different set of PCIE2REG registers.  Accessing the "old" ones
even leads to faults.  There are two surprises though.  One is that it
seems that the interrupt status register always returns 0, and the other
one is that we receive the interrupts way too early, but both can be
worked around for now.