drm/i915/edram: extract i915_edram.[ch] for edram detection

drm/i915/edram: extract i915_edram.[ch] for edram detection

While edram detection ostensibly belongs with the rest of the dram stuff
in soc/intel_dram.c, it's only required by i915 core, not
display. Extract it to a separate i915_edram.[ch] file.

This allows us to drop the edram_size_mb member from struct xe_device.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/612edb7b70755655fbf193ba8af1c539fb93b698.1763578288.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>