ELF: Add ELF program property parsing support

ELF program properties will be needed for detecting whether to
enable optional architecture or ABI features for a new ELF process.

For now, there are no generic properties that we care about, so do
nothing unless CONFIG_ARCH_USE_GNU_PROPERTY=y.

Otherwise, the presence of properties using the PT_PROGRAM_PROPERTY
phdrs entry (if any), and notify each property to the arch code.

For now, the added code is not used.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>