panfrost: don't always build bifrost_compiler

panfrost: don't always build bifrost_compiler

src/panfrost/shared is shared with lima driver, build
bifrost_compiler for lima driver is meaningless and
get link error when only lima driver is enabled.

So only build bifrost_compiler when configued with:
  meson -Dtools=panfrost

Fixes: ec2a59cd7aa4 "panfrost: Move non-Gallium files outside of Gallium"
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Signed-off-by: Qiang Yu <yuq825@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4960>