MAINTAINERS: add Edgar as Xen maintainer

MAINTAINERS: add Edgar as Xen maintainer

Add Edgar as Xen subsystem maintainer in QEMU. Edgar has been a QEMU
maintainer for years, and has already made key changes to one of the
most difficult areas of the Xen subsystem (the mapcache).

Edgar volunteered helping us maintain the Xen subsystem in QEMU and we
are very happy to welcome him to the team. His knowledge and expertise
with QEMU internals will be of great help.

Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Acked-by: Anthony PERARD <anthony@xenproject.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com>