CVE-2026-98928: KVM: arm64: Derive GUEST_HAS_SVE from the SVE feature bit at EL2

In the Linux kernel, the following vulnerability has been resolved:

KVM: arm64: Derive GUESTHASSVE from the SVE feature bit at EL2

pkvminitfeaturesfromhost() takes KVMARCHFLAGGUESTHASSVE and KVMARMVCPUSVE from the host separately, but pkvmvcpuinitsve() tests the bit while vcpuhassve() reads the flag. A host that sets the flag without the bit gets a vCPU with a NULL svestate that the world switch loads the guest's SVE state from.

Derive the flag from the bit, and drop the protected path's copy of the host's flag, which is dead code since protected VMs are not allowed SVE.