create struct for machine initialization arguments

This should help us to:
- More easily add or remove machine initialization arguments without
  having to change every single machine init function;
- More easily make mechanical changes involving the machine init
  functions in the future;
- Let machine initialization forward the init arguments to other
  functions more easily.

This change was half-mechanical process: first the struct was added with
the local ram_size, boot_device, kernel_*, initrd_*, and cpu_model local
variable initialization to all functions. Then the compiler helped me
locate the local variables that are unused, so they could be removed.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

hw/boards.h

@@ -5,12 +5,16 @@
 
 #include "qdev.h"
 
-typedef void QEMUMachineInitFunc(ram_addr_t ram_size,
-                                 const char *boot_device,
-                                 const char *kernel_filename,
-                                 const char *kernel_cmdline,
-                                 const char *initrd_filename,
-                                 const char *cpu_model);
+typedef struct QEMUMachineInitArgs {
+    ram_addr_t ram_size;
+    const char *boot_device;
+    const char *kernel_filename;
+    const char *kernel_cmdline;
+    const char *initrd_filename;
+    const char *cpu_model;
+} QEMUMachineInitArgs;
+
+typedef void QEMUMachineInitFunc(QEMUMachineInitArgs *args);
 
 typedef void QEMUMachineResetFunc(void);