KEYS: Move KEY_LOOKUP_ to include/linux/key.h and define KEY_LOOKUP_ALL

KEYS: Move KEY_LOOKUP_ to include/linux/key.h and define KEY_LOOKUP_ALL

In preparation for the patch that introduces the bpf_lookup_user_key() eBPF
kfunc, move KEY_LOOKUP_ definitions to include/linux/key.h, to be able to
validate the kfunc parameters. Add them to enum key_lookup_flag, so that
all the current ones and the ones defined in the future are automatically
exported through BTF and available to eBPF programs.

Also, add KEY_LOOKUP_ALL to the enum, with the logical OR of currently
defined flags as value, to facilitate checking whether a variable contains
only those flags.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lore.kernel.org/r/20220920075951.929132-7-roberto.sassu@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>