parisc: Allow mmap(MAP_STACK) memory to automatically expand upwards

When userspace allocates memory with mmap() in order to be used for stack,
allow this memory region to automatically expand upwards up until the
current maximum process stack size.
The fault handler checks if the VM_GROWSUP bit is set in the vm_flags field
of a memory area before it allows it to expand.
This patch modifies the parisc specific code only.
A RFC for a generic patch to modify mmap() for all architectures was sent
to the mailing list but did not get enough Acks.

Reported-by: Camm Maguire <camm@maguirefamily.org>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org	# v5.10+