x86/mpparse: Prepare for callback separation

In preparation of splitting the get_smp_config() callback, rename
default_get_smp_config() to mpparse_get_smp_config() and provide an early
and late wrapper.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/r/20240212154639.433811243@linutronix.de