MAINTAINERS: add a maintainer for Microchip / Atmel ECC driver

A new cryptographic engine driver was added in
drivers/crypto/atmel-ecc.*.
Add myself as a maintainer for this driver.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>