bpf: Generalize check_ctx_reg for reuse with other types

mainline inclusion
from mainline-v5.17-rc1
commit be80a1d3
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4WT90
CVE: CVE-2021-4204

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=be80a1d3f9dbe5aee79a325964f7037fe2d92f30



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Generalize the check_ctx_reg() helper function into a more generic named one
so that it can be reused for other register types as well to check whether
their offset is non-zero. No functional change.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Conflicts:
	include/linux/bpf_verifier.h
	kernel/bpf/btf.c
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Reviewed-by: Kuohai Xu <xukuohai@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>