We prefix names with an underscore to make them "safe" C identifiers
when necessary. For example, a value of "32x32" would become "_32x32".
However, when specifying something like
<field ... prefix="BLOCK_SIZE">
<value name="32x32" value="0"/>
</field>
we already have a prefix that makes the field name safe. We'd rather
generate a name with a single underscore, i.e.
#define BLOCK_SIZE_32x32 0
rather than
#define BLOCK_SIZE__32x32 0
This also fixes up affected defines in crocus.
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13809>
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