arm: [MVE intrinsics] Add support for void and load/store pointers as argument types.

arm: [MVE intrinsics] Add support for void and load/store pointers as argument types.

This patch adds support for '_', 'al' and 'as' for void, load pointer
and store pointer argument/return value types in intrinsic signatures.

It also adds a mew memory_scalar_type() helper to function_instance,
which is used by 'al' and 'as'.

2023-11-16  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	* config/arm/arm-mve-builtins-shapes.cc (build_const_pointer):
	New.
	(parse_type): Add support for '_', 'al' and 'as'.
	* config/arm/arm-mve-builtins.h (function_instance): Add
	memory_scalar_type.
	(function_base): Likewise.