tools headers uapi: Sync copy of asm-generic/unistd.h with the kernel sources

tools headers uapi: Sync copy of asm-generic/unistd.h with the kernel sources

To get the changes in:

  b7d624ab4312 asm-generic: unistd.h: fixup broken macro include.
  4e21565b7fd4 asm-generic: add kexec_file_load system call to unistd.h

With this the 'kexec_file_load' syscall will be added to arm64's syscall
table and will appear on the output of 'perf trace' on that platform.

This silences this tools/perf build warning:

  Warning: Kernel ABI header at 'tools/include/uapi/asm-generic/unistd.h' differs from latest version at 'include/uapi/asm-generic/unistd.h'
  diff -u tools/include/uapi/asm-generic/unistd.h include/uapi/asm-generic/unistd.h

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Guo Ren <ren_guo@c-sky.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/n/tip-er8j7qhavtdw0kdga3zswynm@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>