cpu/x86/mp_init: don't wait between INIT and SIPI for X86_AMD_INIT_SIPI

cpu/x86/mp_init: don't wait between INIT and SIPI for X86_AMD_INIT_SIPI

Since current AMD SoCs don't need some wait time between INIT and SIPI,
we can skip the 10ms wait there, which improves the boot time a bit.

before: CPU_CLUSTER: 0 init finished in 632 msecs
after:  CPU_CLUSTER: 0 init finished in 619 msecs

mpinit still works on Mandolin and all CPU cores show up and are usable.
This also doesn't change the binary in a timeless build for boards/SoCs
that don't select X86_AMD_INIT_SIPI which I verified for lenovo/x230.

BUG=b:193885336

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I1e044776f45021742a88a5e369a74383c1baaab6
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56533
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>