[bhnd] fix bcma resource allocation for regions; EROM work around.

• bcma.c - assign different resource IDs for different regions
• bcma_erom.c - workaround for BCM/MIPS bus enumerations

Tested:

• (submitter) Tested on ASUS RT-N16 initially, double checked on ASUS RT-N53
• (landonf) BCM4331

Submitted by: Michael Zhilin <mizkha@gmail.com>
Differential Revision: https://reviews.freebsd.org/D6245