fbio: Use appropriate types for the physical and virtual framebuffer address

Use appropriate types for the physical and virtual framebuffer address.
Fixes framebuffers mapped above 4G physical on 32-bit systems that
support physical address extensions like i386 and Book-E powerpc.

Patch developed by bdragon

Reviewed by: bdragon, luporl
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D28604