drm/i915: Allow control of PSR at runtime through debugfs, v6

drm/i915: Allow control of PSR at runtime through debugfs, v6

Currently tests modify i915.enable_psr and then do a modeset cycle
to change PSR. We can write a value to i915_edp_psr_debug to force
a certain PSR mode without a modeset.

To retain compatibility with older userspace, we also still allow
the override through the module parameter, and add some tracking
to check whether a debugfs mode is specified.

Changes since v1:
- Rename dev_priv->psr.enabled to .dp, and .hw_configured to .enabled.
- Fix i915_psr_debugfs_mode to match the writes to debugfs.
- Rename __i915_edp_psr_write to intel_psr_set_debugfs_mode, simplify
  it and move it to intel_psr.c. This keeps all internals in intel_psr.c
- Perform an interruptible wait for hw completion outside of the psr
  lock, instead of being forced to trywait and return -EBUSY.
Changes since v2:
- Rebase on top of intel_psr changes.
Changes since v3:
- Assign psr.dp during init. (dhnkrn)
- Add prepared bool, which should be used instead of relying on psr.dp. (dhnkrn)
- Fix -EDEADLK handling in debugfs. (dhnkrn)
- Clean up waiting for idle in intel_psr_set_debugfs_mode.
- Print PSR mode when trying to enable PSR. (dhnkrn)
- Move changing psr debug setting to i915_edp_psr_debug_set. (dhnkrn)
Changes since v4:
- Return error in _set() function.
- Change flag values to make them easier to remember. (dhnkrn)
- Only assign psr.dp once. (dhnkrn)
- Only set crtc_state->has_psr on the crtc with psr.dp.
- Fix typo. (dhnkrn)
Changes since v5:
- Only wait for PSR idle on the PSR connector correctly. (dhnkrn)
- Reinstate WARN_ON(drrs.dp) in intel_psr_enable. (dhnkrn)
- Remove stray comment. (dhnkrn)
- Be silent in intel_psr_compute_config on wrong connector. (dhnkrn)

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180809142101.26155-1-maarten.lankhorst@linux.intel.com
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>