MFC 287440:

MFC 287440:
Currently the Linux character device mmap handling only supports mmap
operations that map a single page that has an associated vm_page_t.
This does not permit mapping larger regions (such as a PCI memory
BAR) and it does not permit mapping addresses beyond the top of RAM
(such as a 64-bit BAR located above the top of RAM).

Instead of using a single OBJT_DEVICE object and passing the physaddr via
the offset as a hack, create a new sglist and OBJT_SG object for each
mmap request. The requested memory attribute is applied to the object
thus affecting all pages mapped by the request.

Sponsored by:	Chelsio

git-svn-id: svn://svn.freebsd.org/base/stable/10@287637 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f