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: ec2a59cd "panfrost: Move non-Gallium files outside of Gallium" Signed-off-by: Qiang Yu yuq825@gmail.com