powerpc/book3s64/pkeys: Move pkey related bits in the linux page table

To keep things simple, all the pkey related bits are kept together
in linux page table for 64K config with hash translation. With hash-4k
kernel requires 4 bits to store slots details. This is done by overloading
some of the RPN bits for storing the slot details. Due to this PKEY_BIT0 on
the 4K config is used for storing hash slot details.

64K before

|....|RSV1| RSV2| RSV3 | RSV4 | RPN44| RPN43   |.... | RSV5|
|....| P4 |  P3 |  P2  |  P1  | Busy | HASHPTE |.... |  P0 |

after

|....|RSV1| RSV2| RSV3 | RSV4 | RPN44 | RPN43   |.... | RSV5 |
|....| P4 |  P3 |  P2  |  P1  | P0    | HASHPTE |.... | Busy |

4k before

|....| RSV1 | RSV2     | RSV3 | RSV4 | RPN44| RPN43.... | RSV5|
|....| Busy |  HASHPTE |  P2  |  P1  | F_SEC| F_GIX.... |  P0 |

after

|....| RSV1    | RSV2| RSV3 | RSV4 | Free | RPN43.... | RSV5 |
|....| HASHPTE |  P2 |  P1  |  P0  | F_SEC| F_GIX.... | BUSY |

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200709032946.881753-5-aneesh.kumar@linux.ibm.com