lk2nd: device: menu: possible false positive ARM64 availability

[wonderfulShrineMaidenOfParadise]

Added in #423. Doesn't make much sense to have ARM64 available on msm8909.

Target: msm8909
Device: nokia-leo
lk2nd: 21.0

[TravMurav]

Yeah, this is a bit stupid... I guess this heuristic wasn't the best to use indeed: I guess old firmware couldn't do armv8 scm so we could somewhat reliably use it, however those nokia things are new enough to have more modern firmware despite being 32bit only hw... Not immediately sure if we have a better easy to use heuristic without doing something like hardcoding if each soc is 32 or 64bit...