MAINTAINERS: update email address of Christian Borntraeger

My borntraeger@de.ibm.com email is just a forwarder to the
linux.ibm.com address. Let us remove the extra hop to avoid
a potential source of errors.

While at it, add the relevant email addresses to mailmap.

Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Link: https://lore.kernel.org/r/20211116135803.119489-2-borntraeger@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

.mailmap

@@ -71,6 +71,9 @@ Chao Yu <chao@kernel.org> <chao2.yu@samsung.com>
 Chao Yu <chao@kernel.org> <yuchao0@huawei.com>
 Chris Chiu <chris.chiu@canonical.com> <chiu@endlessm.com>
 Chris Chiu <chris.chiu@canonical.com> <chiu@endlessos.org>
+Christian Borntraeger <borntraeger@linux.ibm.com> <borntraeger@de.ibm.com>
+Christian Borntraeger <borntraeger@linux.ibm.com> <cborntra@de.ibm.com>
+Christian Borntraeger <borntraeger@linux.ibm.com> <borntrae@de.ibm.com>
 Christophe Ricard <christophe.ricard@gmail.com>
 Christoph Hellwig <hch@lst.de>
 Colin Ian King <colin.king@intel.com> <colin.king@canonical.com>

MAINTAINERS

@@ -10445,7 +10445,7 @@ F:	arch/riscv/include/uapi/asm/kvm*
 F:	arch/riscv/kvm/
 
 KERNEL VIRTUAL MACHINE for s390 (KVM/s390)
-M:	Christian Borntraeger <borntraeger@de.ibm.com>
+M:	Christian Borntraeger <borntraeger@linux.ibm.com>
 M:	Janosch Frank <frankja@linux.ibm.com>
 R:	David Hildenbrand <david@redhat.com>
 R:	Claudio Imbrenda <imbrenda@linux.ibm.com>
@@ -16573,7 +16573,7 @@ F:	drivers/video/fbdev/savage/
 S390
 M:	Heiko Carstens <hca@linux.ibm.com>
 M:	Vasily Gorbik <gor@linux.ibm.com>
-M:	Christian Borntraeger <borntraeger@de.ibm.com>
+M:	Christian Borntraeger <borntraeger@linux.ibm.com>
 R:	Alexander Gordeev <agordeev@linux.ibm.com>
 L:	linux-s390@vger.kernel.org
 S:	Supported