.mailmap: Start to use new amd.com email address

.mailmap: Start to use new amd.com email address

Xilinx has been acquired by AMD that's why emails should be also updated.
The patch is updating .mailmap file and also MAINTAINERS files as was done
by commit fa887372f50a ("ppc: qemu: Update MAINTAINERS for correct email
address").
The rest of my emails are not going to change.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>