gallium: switch boolean -> bool at the interface definitions

gallium: switch boolean -> bool at the interface definitions

This is a relatively minimal change to adjust all the gallium interfaces
to use bool instead of boolean. I tried to avoid making unrelated
changes inside of drivers to flip boolean -> bool to reduce the risk of
regressions (the compiler will much more easily allow "dirty" values
inside a char-based boolean than a C99 _Bool).

This has been build-tested on amd64 with:

Gallium drivers: nouveau r300 r600 radeonsi freedreno swrast etnaviv v3d
                 vc4 i915 svga virgl swr panfrost iris lima kmsro
Gallium st:      mesa xa xvmc xvmc vdpau va

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>