powerpc: Rename PTE_SIZE to HPTE_SIZE

It's the size of the hardware PTE; make that clear in the name.

Signed-off-by: Becky Bruce <becky.bruce@freescale.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>