[gdb/tdep] Fix recording of T1 push

[gdb/tdep] Fix recording of T1 push

When running test-case gdb.reverse/recursion.exp on arm-linux with target
board unix/-mthumb, I run into:
...
(gdb) PASS: gdb.reverse/recursion.exp: Skipping recursion from inside
reverse-next^M
bar (x=4195569) at /home/linux/gdb/src/gdb/testsuite/gdb.reverse/recursion.c:34^M
34        int r = foo (x);^M
(gdb) FAIL: gdb.reverse/recursion.exp: print frame when stepping out
...

The problem is the recording of the T1 push instruction [1,2], specifically:
...
000004d8 <foo>:
 4d8:   b580            push    {r7, lr}
...

The current code fails to add a memory record for the memory written with the
value of the lr register.

Fix this by adding the missing memory record.

Tested on arm-linux.

Reviewed-By: Guinevere Larsen <guinevere@redhat.com>
Approved-By: Luis Machado <luis.machado@arm.com>
[1] https://developer.arm.com/documentation/ddi0406/c/Application-Level-Architecture/Instruction-Details/Encoding-of-lists-of-ARM-core-registers
[2] https://developer.arm.com/documentation/ddi0597/2024-09/T32-Instructions-by-Encoding/16-bit?lang=en#pushpop16