drm/i915/ehl: Restrict w/a 1607087056 for EHL/JSL

This w/a is fixed in B0 stepping and needs to be restricted for
A0 stepping only.
Bspec: 33451

Signed-off-by: Swathi Dhanavanthri <swathi.dhanavanthri@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200512180050.6785-1-swathi.dhanavanthri@intel.com