MAINTAINERS: update Liam's email address

Switching to private email address.  Update all contact information

Add an entry to mailmap at the same time.

Link: https://lore.kernel.org/20260422184310.2682901-1-liam@infradead.org
Signed-off-by: Liam R. Howlett <liam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

.mailmap

@@ -496,6 +496,7 @@ Leon Romanovsky <leon@kernel.org> <leon@leon.nu>
 Leon Romanovsky <leon@kernel.org> <leonro@mellanox.com>
 Leon Romanovsky <leon@kernel.org> <leonro@nvidia.com>
 Leo Yan <leo.yan@linux.dev> <leo.yan@linaro.org>
+Liam R. Howlett <liam@infradead.org> <Liam.Howlett@oracle.com>
 Liam Mark <quic_lmark@quicinc.com> <lmark@codeaurora.org>
 Linas Vepstas <linas@austin.ibm.com>
 Linus Lüssing <linus.luessing@c0d3.blue> <linus.luessing@ascom.ch>