MAINTAINERS: Add entry for SPARC architecture
MAINTAINERS: Add entry for SPARC architecture

Add myself as collaborator for the SPARC architecture and its
relevant paths.

Signed-off-by: Martin Åberg <37424e7fbe3f8590d57db5ed6ae5b8866742b6be@gaisler.com>

nashif/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,Vudentz/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,Vudentz/zephyr,galak/zephyr