rockchip: sysreset: update Makefile to work with merged sysreset driver

After applying the merged sysreset driver, there are build failures
due to an out-of-sync Makefile. This updates drivers/sysreset/Makefile
to address these build failures.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>