KVM: arm64: Set IL for injected FPAC exceptions during ERET emulation

KVM: arm64: Set IL for injected FPAC exceptions during ERET emulation

The FPAC syndrome constructed during nested ERET emulation does not set
IL. For FPAC (EC=0x1C), IL reflects the instruction length. ERET and
its authenticated variants are always A64 32-bit instructions, so IL
must be 1.

Fixes: 213b3d1ea161 ("KVM: arm64: nv: Handle ERETA[AB] instructions")
Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260618121643.4105064-5-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>