Add ability for arch code to make changes before we boot

Added a arch_preboot_os() function that cpu specific code can implement to
allow for various modifications to the state of the machine right before
we boot.  This can be useful to setup register state to a specific
configuration.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

common/cmd_bootm.c

@@ -166,6 +166,13 @@ void __arch_lmb_reserve(struct lmb *lmb)
 }
 void arch_lmb_reserve(struct lmb *lmb) __attribute__((weak, alias("__arch_lmb_reserve")));
 
+/* Allow for arch specific config before we boot */
+void __arch_preboot_os(void)
+{
+	/* please define platform specific arch_preboot_os() */
+}
+void arch_preboot_os(void) __attribute__((weak, alias("__arch_preboot_os")));
+
 #if defined(__ARM__)
   #define IH_INITRD_ARCH IH_ARCH_ARM
 #elif defined(__avr32__)
@@ -543,6 +550,7 @@ int do_bootm_subcommand (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 			break;
 		case BOOTM_STATE_OS_GO:
 			disable_interrupts();
+			arch_preboot_os();
 			boot_fn(BOOTM_STATE_OS_GO, argc, argv, &images);
 			break;
 	}
@@ -673,6 +681,8 @@ int do_bootm (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 		return 1;
 	}
 
+	arch_preboot_os();
+
 	boot_fn(0, argc, argv, &images);
 
 	show_boot_progress (-9);