build: Add back _write stub function

The _write stub was removed by this commit:
https://review.trustedfirmware.org/c/TF-M/trusted-firmware-m/+/29175

If a platform does not using the common uart stdout file and
it is compiled with GCC12+, the missing _write function error
will come up.
Add back the weak definition will solve this issue.

Signed-off-by: Dávid Házi <david.hazi@arm.com>
Change-Id: I5303433985e7a7e80f14cd22895eb985e99e6092
1 file changed