drm/amdkfd: Fix GART PTE for non-4K pagesize in svm_migrate_gart_map()

In svm_migrate_gart_map(), while migrating GART mapping, the number of
bytes copied for the GART table only accounts for CPU pages. On non-4K
systems, each CPU page can contain multiple GPU pages, and the GART
requires one 8-byte PTE per GPU page. As a result, an incorrect size was
passed to the DMA, causing only a partial update of the GART table.

Fix this function to work correctly on non-4K page-size systems by
accounting for the number of GPU pages per CPU page when calculating the
number of bytes to be copied.

Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
Signed-off-by: Felix Kuehling <felix.kuehling@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>