[ARM] Move HWCAP_* definitions to asm/elf.h

Move HWCAP_* definitions into asm/elf.h, where they should belong.
Since userspace wants to get at these definitions by including
asm/procinfo.h, include asm/elf.h from this file if __KERNEL__
is not defined, and issue a warning suggesting to fix the program
up to use asm/elf.h instead.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>