Make parsers of capget and capset syscalls self-contained

Make parsers of capget and capset syscalls self-contained

Various versions of <linux/capability.h> used to require different
workarounds to avoid conflicts with types defined by libc headers.
Define all required types and constants locally to fix this issue.

* configure.ac (AC_CHECK_HEADERS): Remove linux/capability.h.
* capability.c: Do not include <linux/capability.h>, remove workarounds
for problematic versions of <linux/capability.h> file.
Define CAP_* and _LINUX_CAPABILITY_VERSION_* constants as enums.
(struct __user_cap_header_struct, struct __user_cap_data_struct): Define.
* xlat/cap_version.in: Add #unconditional.
* xlat/capabilities.in: Likewise.