modesetting: Only use modifiers on kms drivers which do support them.

Use the DRM_CAP_ADDFB2_MODIFIERS query to make sure the kms
driver supports modifiers in the addfb2 ioctl, and fall back
to addfb ioctl without modifiers if modifiers are unsupported.

E.g., as of Linux 4.17, nouveau-kms so far does not suppport
modifiers and gets angry if drmModeAddFB2WithModifiers() is
called (-> failure to set a video mode -> blank screen), but
Mesa's nvc0+ gallium driver causes gbm_bo_get_modifier() to
return a valid modifier by translating the default tiling of
bo's created via gbm_bo_create() into a modifier other than
DRM_FORMAT_MOD_INVALID (see Mesa's nvc0_miptree_get_modifier()).

Testing for != DRM_FORMAT_MOD_INVALID is apparently not
sufficient for safe use of drmModeAddFB2WithModifiers.

Bonus: Handle potential failure of populate_format_modifiers().

The required DRM_CAP is defined since libdrm v2.4.65, and we
require v2.4.89+ for the server, so we can use it unconditionally.

Tested on intel-kms, radeon-kms, nouveau-kms. Fixes failure on
NVidia Pascal.

Fixes: 2f807c23 ("modesetting: Add support for multi-plane pixmaps when page-flipping")
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Reviewed-by: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>