MIPS: Fix some missing CONFIG_CPU_MIPSR6 #ifdefs

MIPS: Fix some missing CONFIG_CPU_MIPSR6 #ifdefs

Commit be0c37c985eddc4 (MIPS: Rearrange PTE bits into fixed positions.)
defines fixed PTE bits for MIPS R2. Then, commit d7b631419b3d230a4d383
(MIPS: pgtable-bits: Fix XPA damage to R6 definitions.) adds the MIPS
R6 definitions in the same way as MIPS R2. But some R6 #ifdefs in the
later commit are missing, so in this patch I fix that.

Signed-off-by: Huacai Chen <[email protected]>
Cc: Aurelien Jarno <[email protected]>
Cc: Steven J. Hill <[email protected]>
Cc: Fuxin Zhang <[email protected]>
Cc: Zhangjin Wu <[email protected]>
Cc: [email protected]
Cc: [email protected]
Patchwork: https://patchwork.linux-mips.org/patch/12164/
Signed-off-by: Ralf Baechle <[email protected]>