i965: Reformat the copyright header in brw_bufmgr.c

i965: Reformat the copyright header in brw_bufmgr.c

This reformats the copyright header to match what we use in most of the
newer parts of the driver.  There are a few minor alterations: we change
"COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS" to the standard
"AUTHORS OR COPYRIGHT HOLDERS", and move the permission notice to the
proper place (it should be in the middle, so "next paragraph" actually
refers to something).

Both of these changes match the OSI's MIT License text:
https://opensource.org/licenses/MIT

I copied this from genX_state_upload.c.