drm/i915: Remove function details from device error messages

Error messages are intended to be addressed to the user; be clear,
succinct, instructive and unambiguous. Adding the function name to
that message does not add any information the user requires and in
the process makes the message less clear.

E.g.

[  245.539711] i915 0000:00:02.0: [drm:i915_gem_init [i915]] Failed to initialize GPU, declaring it wedged!

becomes

[  245.539711] i915 0000:00:02.0: Failed to initialize GPU, declaring it wedged!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180709134858.12446-1-chris@chris-wilson.co.uk