powerpc: Make PPC_64K_PAGES depend on only 44x or PPC_BOOK3S_64

In commit 7820856a

 ("powerpc/mm/book3e/64: Remove unsupported
64Kpage size from 64bit booke") we dropped the 64K page size support
from the 64-bit nohash (Book3E) code.

But we didn't update the dependencies of the PPC_64K_PAGES option,
meaning a randconfig can still trigger this code and cause a build
breakage, eg:
  arch/powerpc/include/asm/nohash/64/pgtable.h:14:2: error: #error "Page size not supported"
  arch/powerpc/include/asm/nohash/mmu-book3e.h:275:2: error: #error Unsupported page size

So remove PPC_BOOK3E_64 from the dependencies. This also means we
don't need to worry about PPC_FSL_BOOK3E, because that was just trying
to prevent the PPC_BOOK3E_64=y && PPC_FSL_BOOK3E=y case.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>