lib/systems: set gcc.arch = "armv6kz", gcc.fpu = "vfpv2" for raspberryPi

>The CPU in the Raspberry Pi 1 and Zero implements the ARMv6 ISA (with VFP2)
https://wiki.debian.org/RaspberryPi#:~:text=The%20CPU%20in%20the%20Raspberry%20Pi,VFP2%29

See also
- https://en.wikipedia.org/wiki/Raspberry_Pi#Specifications
- https://github.com/NixOS/nixpkgs/issues/319036#issuecomment-2232108373

lib/systems/platforms.nix

@@ -201,8 +201,9 @@ rec {
       target = "zImage";
     };
     gcc = {
-      arch = "armv6";
-      fpu = "vfp";
+      # https://en.wikipedia.org/wiki/Raspberry_Pi#Specifications
+      arch = "armv6kz";
+      fpu = "vfpv2";
     };
   };