lib/gnat/i-c.ads: Add `uintptr_t` type

While Ada makes pointers harder to use, it is still useful to provide a
pointer type for use in C interfaces.

Change-Id: I3a30ef0147a459ba82c79a1f85a3d3fb97b0f3a1
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47393
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/lib/gnat/i-c.ads

@@ -59,6 +59,9 @@ package Interfaces.C is
 
    type size_t is mod 2 ** System.Parameters.ptr_bits;
 
+   --  For convenience, also provide an uintptr_t type
+   type uintptr_t is mod 2 ** System.Parameters.ptr_bits;
+
    ----------------------------
    -- Characters and Strings --
    ----------------------------