powerpc: fix build of epapr_paravirt on 64-bit book3s

This fixes an allyesconfig build break introduced by commit
7762b1ed7aaee223230793fcee80672e2e3aa7a8 "powerpc: move epapr paravirt
init of power_save to an initcall".

Signed-off-by: Scott Wood <scottwood@freescale.com>
Cc: Stuart Yoder <stuart.yoder@freescale.com>