CVE-2026-98713: KVM: arm64: Apply the fine-grained UNDEFs without FEAT_FGT

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

KVM: arm64: Apply the fine-grained UNDEFs without FEATFGT

FGUs don't actually require hardware support, so don't gate fgt trap config insertion on FGT. This is the only action required to allow FGUs always, as kvmcalculatetraps() already computes the FGU bits with or without FEATFGT.

This also fixes a spurious WARN when a TLBI OS is run on a guest in vEL1 without FEATTLBIOS on non FEATFGT hardware. In this configuration the course-grained HCREL2.TTLBOS trap reaches the handler handletlbiel1(), which expects an EL1 TLBI only from vEL2. With FGUs enabled the UNDEF will be injected without needing the specific handler.

[oliver: Take Wei-Lin's suggested changelog]