bpf: widen dynptr size/offset to 64 bit

bpf: widen dynptr size/offset to 64 bit

Dynptr currently caps size and offset at 24 bits, which isn’t sufficient
for file-backed use cases; even 32 bits can be limiting. Refactor dynptr
helpers/kfuncs to use 64-bit size and offset, ensuring consistency
across the APIs.

This change does not affect internals of xdp, skb or other dynptrs,
which continue to behave as before. Also it does not break binary
compatibility.

The widening enables large-file access support via dynptr, implemented
in the next patches.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20251026203853.135105-3-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>