drm/i915: Introduce intel_get_buf_trans()

Add a small helper to get the buf trans entris+num_entries
from the struct. Should avoid copy-paste errors in the
platform specific get_buf_trans() functions.

@@
identifier T, N;
@@
- *N = T.num_entries;
- return T.entries;
+ return intel_get_buf_trans(&T, N);

@@
@@
is_hobl_buf_trans(...) { ... }
+
+ static const union intel_ddi_buf_trans_entry *
+ intel_get_buf_trans(const struct intel_ddi_buf_trans *ddi_translations, int *num_entries)
+ {
+	*num_entries = ddi_translations->num_entries;
+	return ddi_translations->entries;
+ }

v2: Handle adl-p

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/20210608073603.2408-7-ville.syrjala@linux.intel.com