cpumask: clean up summit's send_IPI functions

Impact: cleanup, remove cpumask from stack

summit_send_IPI_allbutself might as well call
default_send_IPI_mask_allbutself_logical().  Also change cpumask_t to
struct cpumask and &cpu_online_map to cpu_online_mask while here.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>