tests/fp: Make mul and div tests have a longer timeout

tests/fp: Make mul and div tests have a longer timeout

At the moment we run all fp-test tests except for the muladd ones
with the default meson test timeout of 30s. This is plenty for
most of the test cases, but for multiplication and division we
can sometimes hit the timeout if the CI runner is going slow.

Add support to meson.build for a way to override the timeout on
a per test basis, and use it to set the timeout to 60s for
fp-test-rem, fp-test-div and fp-test-mul. We can use this new
generic mechanism also to set the timeout for mulAdd rather
than hardcoding it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20240917141641.2836265-1-peter.maydell@linaro.org