axs103: Clean-up smp_kick_all_cpus()

 * Rely on default pulse polarity value
 * Don't mess with "multicore" value as it doesn't affect execution

In essence we now do a bare minimal stuff:
 1) Select HS38x2_1 with CORE_SEL=1 bits
 2) Select "manual" core start (via CREG) with START_MODE=0
 3) Generate cpu_start pulse with START=1

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>