linker: ld: correct GNU linker generator output for block linking

Fix the issue that occurs when building with GNU and
CONFIG_LINKER_GENERATOR=y.

Currently, the GROUP {region} directive does not function properly
with GNU. The input section cannot link to the memory group
defined by "zephyr,memory-region" in the final output linker
script.

This commit updates the GNU section name parser script, allowing
it to look up both group and region for output block generation
in the final output linker script.

Signed-off-by: Thinh Le Cong <thinh.le.xr@bp.renesas.com>
Signed-off-by: The Nguyen <the.nguyen.yf@renesas.com>