MAINTAINERS: update arch/arm/mach-davinci

It's time to officially admit I'm not doing anything useful for
mach-davinci anymore.  Since Bartosz is bringing all the code I wrote
10+ years ago into the modern era, he should take over.

Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>