X86: make the SIPI num_starts a config variable

The code to figure out how to set num_starts was
starting to get kludgy. It's a constant for a given
CPU; constants should be constant; make it a config variable.

This change includes an example of how to override it.
Build but not boot tested; drivers welcome.

Change-Id: Iddd906a707bb16251615c7b42f2bfb5a044379b4
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/3796
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marc.jones@se-eng.com>
Reviewed-by: Bruce Griffith <Bruce.Griffith@se-eng.com>
3 files changed