MFC r256814, r256816, r256818, r256846, r256855, r256864 (by nwhitehorn):

MFC r256814, r256816, r256818, r256846, r256855, r256864 (by nwhitehorn):

 - Handle 2GB of ram
 - Allow the OFW interrupt mapping code to work with PCI devices not
   enumerated by Open Firmware, as in the case of FDT.
 - Provide an interface for PCI bus drivers that need some of ofw_pci's
   metadata during attach.
 - Use standard ofw_bus helpers instead of reinventing the wheel.
 - Make hard-wired TLB allocations be at minimum one page.

git-svn-id: svn://svn.freebsd.org/base/stable/10@265954 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f