f2fs: replace gc_urgent_high_remaining with gc_remaining_trials

f2fs: replace gc_urgent_high_remaining with gc_remaining_trials

The user can set the trial count limit for GC urgent and
idle mode with replaced gc_remaining_trials.. If GC thread gets
to the limit, the mode will turn back to GC normal mode finally.

It was applied only to GC_URGENT, while this patch expands it for
GC_IDLE.

Signed-off-by: Yangtao Li <frank.li@vivo.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>