veristat: avoid using kernel-internal headers

Drop linux/compiler.h include, which seems to be needed for ARRAY_SIZE
macro only. Redefine own version of ARRAY_SIZE instead.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230331222405.3468634-4-andrii@kernel.org


Signed-off-by: Alexei Starovoitov <ast@kernel.org>