ARM: multi_v7_defconfig: enable pstore configs

It's useful to get testing on these features on various boards (e.g., on
KernelCI), and (when they're working) the ramoops feature is extremely
helpful for debugging live systems.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>