MAINTAINERS: Add AMD ASF driver entry

Update the MAINTAINERS file with AMD ASF driver details.

Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Acked-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>