Fix "treewide: Consistently call ARM 'arm'"

0c0fad6141 was broken. I didn't realize there's some hidden
metaprogramming code where one can't even grep for 'isFoo' to find its
definition :(

lib/systems/inspect.nix

@@ -11,6 +11,7 @@ rec {
     PowerPC      = { cpu = cpuTypes.powerpc; };
     x86          = { cpu = { family = "x86"; }; };
     Arm          = { cpu = { family = "arm"; }; };
+    Aarch64      = { cpu = { family = "aarch64"; }; };
     Mips         = { cpu = { family = "mips"; }; };
     BigEndian    = { cpu = { significantByte = significantBytes.bigEndian; }; };
     LittleEndian = { cpu = { significantByte = significantBytes.littleEndian; }; };
@@ -28,9 +29,6 @@ rec {
     Windows      = { kernel = kernels.windows; };
     Cygwin       = { kernel = kernels.windows; abi = abis.cygnus; };
     MinGW        = { kernel = kernels.windows; abi = abis.gnu; };
-
-    Arm32        = recursiveUpdate Arm patterns."32bit";
-    Arm64        = recursiveUpdate Arm patterns."64bit";
   };
 
   matchAnyAttrs = patterns:

lib/systems/parse.nix

@@ -40,7 +40,7 @@ rec {
     armv6l   = { bits = 32; significantByte = littleEndian; family = "arm"; };
     armv7a   = { bits = 32; significantByte = littleEndian; family = "arm"; };
     armv7l   = { bits = 32; significantByte = littleEndian; family = "arm"; };
-    aarch64  = { bits = 64; significantByte = littleEndian; family = "arm"; };
+    aarch64  = { bits = 64; significantByte = littleEndian; family = "aarch64"; };
     i686     = { bits = 32; significantByte = littleEndian; family = "x86"; };
     x86_64   = { bits = 64; significantByte = littleEndian; family = "x86"; };
     mips64el = { bits = 32; significantByte = littleEndian; family = "mips"; };