anv: fix number of planes for depth & stencil

We're not counting correctly with depth & stencil images.

Additionally we need to move an assert that is meant just for color
attachments.

v2: Move an assert() (Reported by Craig)
    Change aspect mask checks (Francesco)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: a62a9793 ("anv: enable multiple planes per image/imageView")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105994


Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>
(cherry picked from commit 0a654701)