eBPF.md: Add missing instructions and instruction variants (32-bit jumps, atomic instructions, call and lddw variants)

[qmonnet]

Reflecting the recent addition of 32-bit jump instruction class support to the Linux kernel [0], add the related instructions to the unofficial spec to keep it up-to-date.

[0] merge commit ae575c8a9868 ("Merge branch 'jmp32-insns'") Cc: @JiongWang

[qmonnet]

Now we also want atomic operations. https://lore.kernel.org/bpf/[email protected]/t/#u

[qmonnet]

I updated this PR with more instructions and variants (Cc @dthaler).