Bpf: move under os/linux instead of bits (#6126)

* moved bpf syscall, added some bpf instructions and tests

* had to move bpf out of bits so that a freestanding target could import it

* removed line

* fixed imports

lib/std/os/bits/linux.zig

@@ -24,7 +24,6 @@ pub usingnamespace switch (builtin.arch) {
 };
 
 pub usingnamespace @import("linux/netlink.zig");
-pub const BPF = @import("linux/bpf.zig");
 
 const is_mips = builtin.arch.isMIPS();