sunxi: defconfig: Add pstore support for pinephone

sunxi: defconfig: Add pstore support for pinephone

pstore will allow users to catch kernel crashes and report them to
developers. Modern (Android) phones have pstore usually enabled to get
information about kernel crash, since it's the simplest way to get
kernel backtrace on mobile device without serial console. Usually it's
enabled by default in distribution kernels like Debian.

CONFIG_PSTORE=y
CONFIG_PSTORE_RAM=m

systemd has service that automatically handles pstore and saves them
in /var/lib/pstore for later usage.

In general any DRAM address, that isn't overwritten during a boot is
suitable for pstore.

Range from 0x40000000 - 0x50000000 is heavily used by u-boot for
internal use and to load kernel, fdt, fdto, scripts, pxefile and ramdisk
later in the boot process. Ramdisk start address is 0x4FF00000,
initramfs for kernel with some hacking features and debug info enabled
can take more than 100Mb and final address will be around 0x58000000.
Address 0x61000000 will most likely not overlap with that.

Signed-off-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>