drm/etnaviv: etnaviv_sched: Staticize functions when possible

etnaviv_sched_dependency() and etnaviv_sched_run_job() are only
used in this file, so make them static.

This fixes the following sparse warnings:

drivers/gpu/drm/etnaviv/etnaviv_sched.c:30:18: warning: symbol 'etnaviv_sched_dependency' was not declared. Should it be static?
drivers/gpu/drm/etnaviv/etnaviv_sched.c:81:18: warning: symbol 'etnaviv_sched_run_job' was not declared. Should it be static?

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>