LEON3_MP ISR: shared-IRQ setup overwrite SMP/MP ISR trap handler

Basically the shared-irq handler overwrite the SMP/MP traphandler
previously initialized with set_vector(). That caused IPIs to enter
BSP spurious handler.
LEON3 SMP: CPU ack irq on trap vector entry execution
LEON3 SMP: remove compiler warning from __delay() declaration
SPARC BSPs: disable interrupts as early as possible

There is no point having interrupts enabled before reaching
boot_card() that disables interrupt. We better have it off
all the time.

It is required to turn off interrupt on secondary CPUs in an
SMP system.