toolchain/toolchain-external: update Arm aarch64 toolchain to 12.3.rel1

Update the aarch64 toolchain to 12.3.rel1 that includes update to gcc
12.3, gdb 13, binutils 2.40, and glibc 2.37.

Signed-off-by: Vivek Gautam <vivek.gautam@arm.com>