powerpc/e500: encode hugepage size in PTE bits

powerpc/e500: encode hugepage size in PTE bits

Use PTE page size bits to encode hugepage size with the following format
corresponding to the values expected in bits 52-55 in MAS1 register.
Those bits are called TSIZE:
	0001 	4 Kbyte
	0010 	16 Kbyte
	0011 	64 Kbyte
	0100 	256 Kbyte
	0101 	1 Mbyte
	0110 	4 Mbyte
	0111 	16 Mbyte
	1000 	64 Mbyte
	1001 	256 Mbyte
	1010 	1 Gbyte
	1011 	4 Gbyte
	1100 	16 Gbyte
	1101	64 Gbyte
	1110	256 Gbyte
	1111	1 Tbyte

It corresponds to shift value minus 10 with lowest bit removed.

It is not the value expected in the PTE in that field, but only e6500
performs HW based TLB loading and the e6500 reference manual explicitely
says that this field is ignored.

Also add pte_huge_size() which will be used later.

Link: https://lkml.kernel.org/r/6f7ce82fa8c381d55f65342d77060fc55802e612.1719928057.git.christophe.leroy@csgroup.eu
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>