powerpc/32s: Fix BATs setting with CONFIG_STRICT_KERNEL_RWX

powerpc/32s: Fix BATs setting with CONFIG_STRICT_KERNEL_RWX

Serge reported some crashes with CONFIG_STRICT_KERNEL_RWX enabled
on a book3s32 machine.

Analysis shows two issues:
  - BATs addresses and sizes are not properly aligned.
  - There is a gap between the last address covered by BATs and the
    first address covered by pages.

Memory mapped with DBATs:
0: 0xc0000000-0xc07fffff 0x00000000 Kernel RO coherent
1: 0xc0800000-0xc0bfffff 0x00800000 Kernel RO coherent
2: 0xc0c00000-0xc13fffff 0x00c00000 Kernel RW coherent
3: 0xc1400000-0xc23fffff 0x01400000 Kernel RW coherent
4: 0xc2400000-0xc43fffff 0x02400000 Kernel RW coherent
5: 0xc4400000-0xc83fffff 0x04400000 Kernel RW coherent
6: 0xc8400000-0xd03fffff 0x08400000 Kernel RW coherent
7: 0xd0400000-0xe03fffff 0x10400000 Kernel RW coherent

Memory mapped with pages:
0xe1000000-0xefffffff  0x21000000       240M        rw       present           dirty  accessed

This patch fixes both issues. With the patch, we get the following
which is as expected:

Memory mapped with DBATs:
0: 0xc0000000-0xc07fffff 0x00000000 Kernel RO coherent
1: 0xc0800000-0xc0bfffff 0x00800000 Kernel RO coherent
2: 0xc0c00000-0xc0ffffff 0x00c00000 Kernel RW coherent
3: 0xc1000000-0xc1ffffff 0x01000000 Kernel RW coherent
4: 0xc2000000-0xc3ffffff 0x02000000 Kernel RW coherent
5: 0xc4000000-0xc7ffffff 0x04000000 Kernel RW coherent
6: 0xc8000000-0xcfffffff 0x08000000 Kernel RW coherent
7: 0xd0000000-0xdfffffff 0x10000000 Kernel RW coherent

Memory mapped with pages:
0xe0000000-0xefffffff  0x20000000       256M        rw       present           dirty  accessed

Fixes: 63b2bc619565 ("powerpc/mm/32s: Use BATs for STRICT_KERNEL_RWX")
Reported-by: Serge Belyshev <belyshev@depni.sinp.msu.ru>
Acked-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>