[bhnd] Add remaining bus_(read|write|set)_(1|2|4) APIs

This adds bhnd-compatible implementations of bus_(read|write|set)_(1|2|4) APIs,
and upgrades the SPROM parsing code to use bhnd_bus_read_region_stream_2().

This a precursor to bridge support for resource adjustment and the new
ChipCommon bus support.

Tested:

• Tested against BCM4331
• Kernel build verified via tinderbox.

Submitted by: Landon Fuller <landonf@landonf.org>
Differential Revision: https://reviews.freebsd.org/D6469