arm64: smp: Increase secondary CPU boot timeout value

When many debug options are enabled simultaneously (e.g. PROVE_LOCKING,
KMEMLEAK, DEBUG_PAGE_ALLOC, KASAN etc), it is possible for us to timeout
when attempting to boot a secondary CPU and give up. Unfortunately, the
CPU will /eventually/ appear, and sit in the background happily stuck
in a recursive exception due to a NULL stack pointer.

Increase the timeout to 5s, which will of course be enough for anybody.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>