tools/x86/kcpuid: Fix error handling

tools/x86/kcpuid: Fix error handling

Error handling in kcpuid is unreliable.  On malloc() failures, the code
prints an error then just goes on.  The error messages are also printed
to standard output instead of standard error.

Use err() and errx() from <err.h> to direct all error messages to
standard error and automatically exit the program.  Use err() to include
the errno information, and errx() otherwise.  Use warnx() for warnings.

While at it, alphabetically reorder the header includes.

[ mingo: Fix capitalization in the help text while at it. ]

Fixes: c6b2f240bf8d ("tools/x86: Add a kcpuid tool to show raw CPU features")
Reported-by: Remington Brasga <rbrasga@uci.edu>
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20250324142042.29010-2-darwi@linutronix.de
Closes: https://lkml.kernel.org/r/20240926223557.2048-1-rbrasga@uci.edu