elf: Define note name macros

elf: Define note name macros

elf.h had a comment saying:
> Notes used in ET_CORE. Architectures export some of the arch register
> sets using the corresponding note types via the PTRACE_GETREGSET and
> PTRACE_SETREGSET requests.
> The note name for these types is "LINUX", except NT_PRFPREG that is
> named "CORE".

However, NT_PRSTATUS is also named "CORE". It is also unclear what
"these types" refers to.

To fix these problems, define a name for each note type. The added
definitions are macros so the kernel and userspace can directly refer to
them to remove their duplicate definitions of note names.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Acked-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Link: https://lore.kernel.org/r/20250115-elf-v5-1-0f9e55bbb2fc@daynix.com
Signed-off-by: Kees Cook <kees@kernel.org>