drm/i915: Include intel_de_{read,write}_fw() in i915_reg_rw traces

We lost the i915_reg_rw tracepoint for a lot of display registers
when we switched from the heavyweight normal register accessors to
the lightweight _fw() variants. See eg. commit dd584fc0
("drm/i915: Use I915_READ_FW for plane updates").

Put the tracepoints back so that the register traces might
actually be useful. Hopefully these should be close to free
when the tracepoint is not enabled and thus not slow down
our vblank critical sections significantly.

v2: Copy paste the same-cacheline-hang warning from
    intel_uncore.h (Anshuman)

Cc: Cooper Chiou <cooper.chiou@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210430143945.6776-2-ville.syrjala@linux.intel.com