kernel: Use the stock xiaomi-sdm845 config for /proc/config.gz

Userspace reads /proc/config.gz and spits out an error message after boot
finishes when it doesn't like the kernel's configuration. In order to
preserve our freedom to customize the kernel however we'd like, show
userspace the stock config so that it never complains about our
kernel configuration.

Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Change-Id: I940e19ac6eb6079c724da474b48e6ce43d2086ad

Author: kerneltoast