linux-postmarketos-qcom-sdm845: update to v5.11

Update the SDM845 linux package to Linux 5.11, this also includes various improvements and fixes compile warnings.

I've also added a make olddefconfig to the APKBUILD so that the compiler/host specific options get fixed before the build starts. If the .config is generated with clang then the build will get stuck prompting the user to select "NEW" config options for gcc without this fix.