iris: Assert against FCV_CCS_E for blitter writes

iris: Assert against FCV_CCS_E for blitter writes

The FCV feature is documented to occur on regular render writes. Blitter
writes don't fall under that category. So, if the destination resource
of a blitter write had the FCV aux usage, we would have a good reason to
change the aux usage of the access to plain CCS_E.

We don't actually need to write code to handle this. iris doesn't use
any compression on blitter writes. Make that obvious with an assert.

Reviewed-by: Rohan Garg <rohan.garg@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23220>