panfrost: Cleanup shader upload code

panfrost: Cleanup shader upload code

The old algorithm is still used (and the same issue -- namely, leaking
all shaders -- applies) but we're way more concise about it since we're
*only* using the routine for shaders nowadays; everything else is a
BO-proper or transient.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>