drm/i915: use explicit includes for i915_reg.h and i915_irq.h

A lot of places include i915_reg.h implicitly via i915_irq.h, which gets
included implicitly via intel_display_trace.h. Remove the includes from
the headers, and include i915_reg.h and i915_irq.h explicitly where
needed.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230419094243.366821-1-jani.nikula@intel.com