bpf: remove CONFIG_BPF_JIT dependency on CONFIG_MODULES of

BPF just-in-time compiler depended on CONFIG_MODULES because it used
module_alloc() to allocate memory for the generated code.

Since code allocations are now implemented with execmem, drop dependency of
CONFIG_BPF_JIT on CONFIG_MODULES and make it select CONFIG_EXECMEM.

Suggested-by: Björn Töpel <bjorn@kernel.org>
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>