board: am57xx: MAINTAINERS: Update for current maintainer

Felipe Balbi has move on from TI and the current email ID is no longer
valid. So, replacing with Lokesh.

While at it, update missing config file which was untracked.

Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>