For formats that are supported only with non-linear modifiers it
doesn't make to much sense to define cpp or char_per_block, so that
will be set to 0.

This patch adds a restriction to force having a modifier attached when
cpp/char_per_block is 0, and to bypass checking the pitch restriction.

This had been discussed here.
[1] https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&highlight_names=&date=2018-09-13&show_html=trueReviewed-by: Brian Starkey <brian.starkey@arm.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181101151051.1509-5-alexandru-cosmin.gheorghe@arm.com