bpf: Convert PTR_TO_MEM_OR_NULL to composable types.

mainline inclusion
from mainline-v5.17-rc1
commit cf9f2f8d
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4WRPV
CVE: CVE-2022-0500

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cf9f2f8d62eca810afbd1ee6cc0800202b000e57

--------------------------------

Remove PTR_TO_MEM_OR_NULL and replace it with PTR_TO_MEM combined with
flag PTR_MAYBE_NULL.
Signed-off-by: NHao Luo <haoluo@google.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211217003152.48334-7-haoluo@google.com
Conflicts:
	kernel/bpf/btf.c
	kernel/bpf/verifier.c
Signed-off-by: NPu Lehui <pulehui@huawei.com>
Reviewed-by: NKuohai Xu <xukuohai@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

include/linux/bpf.h

@@ -456,7 +456,6 @@ enum bpf_reg_type {
 	PTR_TO_SOCK_COMMON_OR_NULL	= PTR_MAYBE_NULL | PTR_TO_SOCK_COMMON,
 	PTR_TO_TCP_SOCK_OR_NULL		= PTR_MAYBE_NULL | PTR_TO_TCP_SOCK,
 	PTR_TO_BTF_ID_OR_NULL		= PTR_MAYBE_NULL | PTR_TO_BTF_ID,
-	PTR_TO_MEM_OR_NULL		= PTR_MAYBE_NULL | PTR_TO_MEM,
 
 	/* This must be the last entry. Its purpose is to ensure the enum is
 	 * wide enough to hold the higher bits reserved for bpf_type_flag.