kselftest/arm64: Allow epoll_wait() to return more than one result

kselftest/arm64: Allow epoll_wait() to return more than one result

When everything is starting up we are likely to have a lot of child
processes producing output at once.  This means that we can reduce
overhead a bit by allowing epoll_wait() to return more than one
descriptor at once, it cuts down on the number of system calls we need
to do which on virtual platforms where the syscall overhead is a bit
more noticable and we're likely to have a lot more children active can
make a small but noticable difference.

On physical platforms the relatively small number of processes being run
and vastly improved speeds push the effects of this change into the
noise.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221129215926.442895-4-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>