KVM: x86: Remove unnecessary caching of KVM's PV CPUID base

Now that KVM only searches for KVM's PV CPUID base when userspace sets
guest CPUID, drop the cache and simply do the search every time.

Practically speaking, this is a nop except for situations where userspace
sets CPUID _after_ running the vCPU, which is anything but a hot path,
e.g. QEMU does so only when hotplugging a vCPU.  And on the flip side,
caching guest CPUID information, especially information that is used to
query/modify _other_ CPUID state, is inherently dangerous as it's all too
easy to use stale information, i.e. KVM should only cache CPUID state when
the performance and/or programming benefits justify it.

Link: https://lore.kernel.org/r/20241128013424.4096668-34-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>