panfrost: Properly align stride

Handle buffers whose width is not aligned to 16px by padding the stride
and storing it accordingly.

This does not reject imports for images whose stride is not sufficiently
aligned.

v2: make sure bo->stride is set on imported buffers, and add missing
variable definition. (Tomeu)

Tested-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
21 jobs for !467 with panfrost-stride-align in 21 minutes and 43 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Containers Build
passed #179819
ubuntu

00:00:34

 
  Build+Test
passed #179833
make-gallium-drivers-other

00:11:37

passed #179832
make-gallium-drivers-radeonsi

00:09:04

passed #179831
make-gallium-drivers-swr

00:14:44

passed #179834
make-gallium-st-clover-llvm

00:10:46

passed #179835
make-gallium-st-clover-llvm-39

00:10:05

passed #179836
make-gallium-st-other

00:09:03

passed #179830
make-loader-classic-dri

00:12:49

passed #179829
make-vulkan

00:07:55

passed #179826
meson-gallium-clover-llvm

00:03:44

passed #179827
meson-gallium-clover-llvm39

00:03:19

passed #179825
meson-gallium-drivers-other

00:08:49

passed #179824
meson-gallium-radeonsi

00:02:03

passed #179828
meson-gallium-st-other

00:04:11

passed #179823
meson-gallium-swr

00:10:10

passed #179822
meson-glvnd

00:06:41

passed #179821
meson-loader-classic-dri

00:06:36

passed #179820
meson-vulkan

00:03:50

passed #179838
scons-llvm

00:05:04

passed #179837
scons-nollvm

00:06:13

passed #179839
scons-swr

00:06:54