intel/ppgtt: memory address alignment

Kernel (for ppgtt) requires memory address to be
aligned to page size (4096).

-v2: added marking that also fixes initial commit 01058a5522.
-v3: numbers replaced by PAGE_SIZE; buffer-object size is aligned
instead of alignment of offsets (Chris Wilson).
-v4: changes related to PAGE_SIZE moved to separate commit
-v5: restored alignment to page-size for 0-size.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106997
Fixes: a363bb2cd0 (i965: Allocate VMA in userspace for full-PPGTT systems.)
Fixes: 01058a5522 (i965: Add virtual memory allocator infrastructure to brw_bufmgr.)
Signed-off-by: Sergii Romantsov <sergii.romantsov@globallogic.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit 24839663a4)

src/mesa/drivers/dri/i965/brw_bufmgr.c

@@ -496,7 +496,6 @@ bo_alloc_internal(struct brw_bufmgr *bufmgr,
                   uint32_t stride)
 {
    struct brw_bo *bo;
-   unsigned int page_size = getpagesize();
    int ret;
    struct bo_cache_bucket *bucket;
    bool alloc_from_cache;
@@ -522,12 +521,12 @@ bo_alloc_internal(struct brw_bufmgr *bufmgr,
     * allocation up.
     */
    if (bucket == NULL) {
-      bo_size = size;
-      if (bo_size < page_size)
-         bo_size = page_size;
+      unsigned int page_size = getpagesize();
+      bo_size = size == 0 ? page_size : ALIGN(size, page_size);
    } else {
       bo_size = bucket->size;
    }
+   assert(bo_size);
 
    mtx_lock(&bufmgr->lock);
    /* Get a buffer out of the cache if available */