x86/cacheinfo: Properly parse CPUID(0x80000006) L2/L3 associativity

x86/cacheinfo: Properly parse CPUID(0x80000006) L2/L3 associativity

Complete the AMD CPUID(4) emulation logic, which uses CPUID(0x80000006)
for L2/L3 cache info and an assocs[] associativity mapping array, by
adding entries for 3-way caches and 6-way caches.

Properly handle the case where CPUID(0x80000006) returns an L2/L3
associativity of 9.  This is not real associativity, but a marker to
indicate that the respective L2/L3 cache information should be retrieved
from CPUID(0x8000001d) instead.  If such a marker is encountered, return
early from legacy_amd_cpuid4(), thus effectively emulating an "invalid
index" CPUID(4) response with a cache type of zero.

When checking if CPUID(0x80000006) L2/L3 cache info output is valid, and
given the associtivity marker 9 above, do not just check if the whole
ECX/EDX register is zero.  Rather, check if the associativity is zero or
9.  An associativity of zero implies no L2/L3 cache, which make it the
more correct check anyway vs. a zero check of the whole output register.

Fixes: a326e948c538 ("x86, cacheinfo: Fixup L3 cache information for AMD multi-node processors")
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: x86-cpuid@lists.linux.dev
Link: https://lore.kernel.org/r/20250409122233.1058601-3-darwi@linutronix.de