uart: Add ACPI entry for LS1046A UART

NXP defines unique name for LS1046A UART - "NXP0018".
It is ns8250 compatible, adding a new uart compat data entry is enough
to make it work.
Tested on LS1046ARDB.

Approved by: mw(mentor)
Reviewed by: mw, kd
Obtained from: Semihalf
Differential Revision: https://reviews.freebsd.org/D36260