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/shix.c

@@ -37,11 +37,9 @@
 #define BIOS_FILENAME "shix_bios.bin"
 #define BIOS_ADDRESS 0xA0000000
 
-static void shix_init(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)
+static void shix_init(QEMUMachineInitArgs *args)
 {
+    const char *cpu_model = args->cpu_model;
     int ret;
     CPUSH4State *env;
     struct SH7750State *s;