pipe-loader: drop support for non-render node devices

pipe-loader: drop support for non-render node devices

Render nodes have been around for quite some time. Removing support via
the master/primary node allows us to clean up the conditional
compilation and simplify the build greatly.

For example currently we the pipe-loader, which explicitly links against
xcb and friends (for X auth) if found at compile-time. That
would cause problems as one will be forced to use X/xcb, even if it's a
headless system that is used for opencl.

v2: Clarify the linking topic in the commit message.

Cc: Tom Stellard <thomas.stellard@amd.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>