mips: adjust brk randomization offset to fit generic version

mips: adjust brk randomization offset to fit generic version

This commit simply bumps up to 32MB and 1GB the random offset of brk,
compared to 8MB and 256MB, for 32bit and 64bit respectively.

Link: http://lkml.kernel.org/r/20190730055113.23635-12-alex@ghiti.fr
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Acked-by: Paul Burton <paul.burton@mips.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: James Hogan <jhogan@kernel.org>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>