mips/kvm: Init EBase to correct KSEG0

mips/kvm: Init EBase to correct KSEG0

The EBase CP0 register is initialised to 0x80000000, however with KVM
the guest's KSEG0 is at 0x40000000. The incorrect value doesn't get
passed to KVM yet as KVM doesn't implement the EBase register, however
we should set it correctly now so as not to break migration/loadvm to a
future version of QEMU that does support EBase.

Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>