This patch provides debugfs interface i915_guc_output_control for
on the fly enabling/disabling of logging in GuC firmware and controlling
the verbosity level of logs.
The value written to the file, should have bit 0 set to enable logging and
bits 4-7 should contain the verbosity info.
v2: Add a forceful flush, to collect left over logs, on disabling logging.
Useful for Validation.
v3: Besides minor cleanup, implement read method for the debugfs file and
set the guc_log_level to -1 when logging is disabled. (Tvrtko)
v4: Minor cleanup & rebase. (Tvrtko)
v5:
- Lock struct_mutex after the NULL check for guc log buffer vma. (Chris)
- Rebase.