tests/functional: Bump up arm_replay timeout

On my machine the arm_replay test takes over 2 minutes to run
in a config with Rust enabled and debug enabled:

$ time (cd build/rust ; PYTHONPATH=../../python:../../tests/functional
QEMU_TEST_QEMU_BINARY=./qemu-system-arm ./pyvenv/bin/python3
../../tests/functional/test_arm_replay.py)
TAP version 13
ok 1 test_arm_replay.ArmReplay.test_cubieboard
ok 2 test_arm_replay.ArmReplay.test_vexpressa9
ok 3 test_arm_replay.ArmReplay.test_virt
1..3

real    2m16.564s
user    2m13.461s
sys     0m3.523s

Bump up the timeout to 4 minutes.

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Message-id: [email protected]

Author: pm215