xen: update ECLAIR service identifiers from MC3R1 to MC3A2.

xen: update ECLAIR service identifiers from MC3R1 to MC3A2.

Rename all instances of ECLAIR MISRA C:2012 service identifiers,
identified by the prefix MC3R1, to use the prefix MC3A2, which
refers to MISRA C:2012 Amendment 2 guidelines.

This update is motivated by the need to upgrade ECLAIR GitLab runners
that use the new naming scheme for MISRA C:2012 Amendment 2 guidelines.

Changes to the docs/misra directory are needed in order to keep
comment-based deviation up to date.

Signed-off-by: Alessandro Zucchelli <alessandro.zucchelli@bugseng.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>