riscv: Fix fast_unaligned_access_speed_key not getting initialized

The static key fast_unaligned_access_speed_key is supposed to be
initialized after check_unaligned_access_all_cpus() has been completed.

However, check_unaligned_access_all_cpus() has been moved to late_initcall
while setting fast_unaligned_access_speed_key still happens at
arch_initcall_sync, thus the static key does not get properly initialized.

fast_unaligned_access_speed_key can still be initialized in CPU hotplug
events, but that cannot be relied on.

Move fast_unaligned_access_speed_key's initialization into
check_unaligned_access_all_cpus() to fix this issue. This also prevent
someone from moving one initcall while forgetting the other in the future.

Fixes: 6455c6c11827 ("riscv: Clean up & optimize unaligned scalar access probe")
Reported-by: Michael Neuling <mikey@neuling.org>
Closes: https://lore.kernel.org/linux-riscv/CAEjGV6y0=bSLp_wrS0uHFj1S2TCRtz4GKzaU5O-L1VV-EL7Nnw@mail.gmail.com/
Signed-off-by: Nam Cao <namcao@linutronix.de>
Link: https://patch.msgid.link/20260407120639.4006031-1-namcao@linutronix.de
Signed-off-by: Paul Walmsley <pjw@kernel.org>