drm/radeon: add PX quirk for Asus K73TK

commit b1550359d1eb392ee54f7cf47cffcfe0a602f6a7 upstream.

With this the dGPU turns on correctly.

Signed-off-by: Nico Sneck <nicosneck@hotmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>