panfrost: Remove unneeded pmap_zero_page() calls

For a few years now, VM_ALLOC_ZERO means, "please zero the returned pages",
so these calls are redundant.  Remove them.

Author: markjdb

sys/dev/drm/freebsd/drm_gem_cma_helper.c

@@ -105,8 +105,6 @@ drm_gem_cma_alloc_contig(size_t npages, u_long alignment, vm_memattr_t memattr,
 	}
 
 	for (i = 0; i < npages; i++, m++) {
-		if ((m->flags & PG_ZERO) == 0)
-			pmap_zero_page(m);
 		m->valid = VM_PAGE_BITS_ALL;
 		(*ret_page)[i] = m;
 	}

sys/dev/drm/panfrost/panfrost_gem.c

@@ -607,8 +607,6 @@ panfrost_alloc_pages_iommu(struct panfrost_gem_object *bo)
 
 			return (ENOMEM);
 		}
-		if ((m->flags & PG_ZERO) == 0)
-			pmap_zero_page(m);
 		va = PHYS_TO_DMAP(VM_PAGE_TO_PHYS(m));
 		cpu_dcache_wb_range((void *)va, PAGE_SIZE);
 		m->valid = VM_PAGE_BITS_ALL;
@@ -654,8 +652,6 @@ panfrost_alloc_pages_contig(struct panfrost_gem_object *bo)
 		return (ENOMEM);
 	}
 	for (i = 0; i < bo->npages; i++) {
-		if ((m->flags & PG_ZERO) == 0)
-			pmap_zero_page(m);
 		va = PHYS_TO_DMAP(VM_PAGE_TO_PHYS(m));
 		cpu_dcache_wb_range((void *)va, PAGE_SIZE);
 		m->valid = VM_PAGE_BITS_ALL;