Adjust handling of package infos.

* add HAIKU_PACKAGING_ARCH, which is set to the target packaging 
  architecture
* introduce support for generic package infos, which are package infos
  that are the same for all architectures, except for the declaration
  of the package architecture itself
* move package info files underneath architecture-specific or generic
  folder

src/data/package_infos/generic/haiku_cross_devel

@@ -1,6 +1,6 @@
 name			haiku_cross_devel
 version			R1~alpha4_pm-1
-architecture	x86_gcc2
+architecture	HAIKU_PACKAGING_ARCH
 summary			"The Haiku base system files for cross development"
 
 description		"The package contains all files associated with the base system

src/data/package_infos/generic/haiku_devel

@@ -1,6 +1,6 @@
 name			haiku_devel
 version			R1~alpha4_pm-1
-architecture	x86_gcc2
+architecture	HAIKU_PACKAGING_ARCH
 summary			"The Haiku base system development files"
 
 description		"The package contains all files associated with the base system

src/data/package_infos/generic/haiku_loader

@@ -1,6 +1,6 @@
 name			haiku_loader
 version			R1~alpha4_pm-1
-architecture	x86_gcc2
+architecture	HAIKU_PACKAGING_ARCH
 summary			"The Haiku boot loader"
 description		"The Haiku boot loader."