MAINTAINERS: Add keystone git tree information
MAINTAINERS: Add keystone git tree information

Update the Keystone entry to add git tree information.

Signed-off-by: Santosh Shilimkar <5b4d8dc9ea337fff5fd1729321eda9873ade0b09@ti.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs