Changes to kernel_args to make it identical for x86 and x86_64.

* Added a FixedWidthPointer template class which uses 64-bit storage to hold
  a pointer. This is used in place of raw pointers in kernel_args.
* Added __attribute__((packed)) to kernel_args and all structures contained
  within it. This is necessary due to different alignment behaviour for
  32-bit and 64-bit compilation with GCC.
* With these changes, kernel_args will now come out the same size for both
  the x86_64 kernel and the loader, excluding the preloaded_image structure
  which has not yet been changed.
* Tested both an x86 GCC2 and GCC4 build, no problems caused by these changes.

headers/private/kernel/boot/platform/bios_ia32/platform_kernel_args.h

@@ -12,6 +12,7 @@
 
 #include <arch/x86/apm.h>
 #include <bios_drive.h>
+#include <util/FixedWidthPointer.h>
 
 
 // must match SMP_MAX_CPUS in arch_smp.h
@@ -25,9 +26,10 @@
 typedef struct {
 	uint16		serial_base_ports[MAX_SERIAL_PORTS];
 
-	bios_drive	*drives;	// this does not contain the boot drive
+	FixedWidthPointer<bios_drive> drives;
+		// this does not contain the boot drive
 
 	apm_info	apm;
-} platform_kernel_args;
+} _PACKED platform_kernel_args;
 
 #endif	/* KERNEL_BOOT_PLATFORM_BIOS_IA32_KERNEL_ARGS_H */