automake: remove no longer needed HAVE_LOADER_GALLIUM conditional

automake: remove no longer needed HAVE_LOADER_GALLIUM conditional

As of last few commits we have a static and dynamic pipe-loader. Either
of which will be used with (almost) all targets..

We can look into allowing the user to select which way the targets are
built, be that 'static for all' or 'per target' in follow up commits.
After which we can look into building only the static or dynamic
version, although building both shouldn't cause any issues.

Hack/workaround alert:
Control the standalone pipe-drivers via HAVE_CLOVER. Will need to be
fixed as the targets are converted/configure knobs are in.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Rob Clark <robclark@freedesktop.org>