arm: Add declarations to avoid needing to include headers

At present common.h includes various ARM-specific headers. In preparation
for dropping this, add a few explicit declarations.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/arm/include/asm/bootm.h

@@ -41,6 +41,7 @@ extern void udc_disconnect(void);
  #define BOOTM_ENABLE_INITRD_TAG	0
 #endif
 
+struct tag_serialnr;
 #ifdef CONFIG_SERIAL_TAG
  #define BOOTM_ENABLE_SERIAL_TAG	1
 void get_board_serial(struct tag_serialnr *serialnr);

arch/arm/include/asm/u-boot-arm.h

@@ -47,6 +47,8 @@ ulong	get_timer_masked	(void);
 void	udelay_masked		(unsigned long usec);
 
 /* calls to c from vectors.S */
+struct pt_regs;
+
 void bad_mode(void);
 void do_undefined_instruction(struct pt_regs *pt_regs);
 void do_software_interrupt(struct pt_regs *pt_regs);

arch/arm/lib/bootm.c

@@ -31,6 +31,7 @@
 #ifdef CONFIG_ARMV7_NONSEC
 #include <asm/armv7.h>
 #endif
+#include <asm/setup.h>
 
 DECLARE_GLOBAL_DATA_PTR;