bpf: move memory size checks to bpf_map_charge_init()

Most bpf map types doing similar checks and bytes to pages
conversion during memory allocation and charging.

Let's unify these checks by moving them into bpf_map_charge_init().

Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>