smp: Fix smp race introduced in 0673b787

smp: Fix smp race introduced in 0673b787

In 0673b787 the QEMU SMP init code was changed to run in 32bit mode.
Unfortunately, the transition32 assembler function is not
multi-processor safe, because it modifies the global RTC index
register.  This race condition led to sporadic failures when emulating
machines with a large number of processors.

This patch changes the entry_smp code to use a variant of transition32
that does not touch the RTC registers.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
(cherry picked from commit 5ae3dd6f74e17a7cd06165a75214798b0c606115)