KVM: make asm-generic/kvm_para.h have an ifdef __KERNEL__ block

There are two functions in this asm-generic file.  Looking at
other arch which do not use the generic version, these two fcns
are within an #ifdef __KERNEL__ block, so make the generic one
consistent with those.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Avi Kivity <avi@redhat.com>