Cleanup the interface in preparation for hierarchical page tables.

v2: add incr parameter to set_page for simple scattered PTs uptates
    added PDE-specific flags to r600_flags and radeon_drm.h
    removed superfluous value masking with 0xffffffff

v3: removed superfluous bo_va->valid checking
    changed R600_PTE_VALID to R600_ENTRY_VALID to handle PDE too

v4 (ck): fix indention style, rework and fix typos in commit message,
         add documentation for incr parameter, also use incr
         parameter for system pages

v5 (agd5f): use upper_32_bits() and minor white space fixes
Signed-off-by: Christian König <deathsimple@vodafone.de>
Signed-off-by: Dmitry Cherkassov <Dmitrii.Cherkasov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>