arm/arm64: Generalize wfe/sev names in smp.c

Most of Arm's on_cpus() implementation can be shared by any
architecture which has the possible, present, and idle cpumasks,
like riscv does. Rename the exceptions (wfe/sve) to something
more generic in order to prepare to share the functions.

Signed-off-by: Andrew Jones <andrew.jones@linux.dev>
Acked-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>