x86: drop Xeon Phi support

Do as was decided in Lisbon. Reportedly Xen hasn't been working very
well on those processors anyway.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-By: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

CHANGELOG.md

@@ -11,6 +11,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Added
 
 ### Removed
+ - On x86:
+   - Support for running on Xeon Phi processors.
 
 ## [4.19.0](https://xenbits.xenproject.org/gitweb/?p=xen.git;a=shortlog;h=RELEASE-4.19.0) - 2024-07-29