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>
diff --git a/arch/arm/include/asm/bootm.h b/arch/arm/include/asm/bootm.h
index 436c35a..4c9bb86 100644
--- a/arch/arm/include/asm/bootm.h
+++ b/arch/arm/include/asm/bootm.h
@@ -41,6 +41,7 @@
  #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);
diff --git a/arch/arm/include/asm/u-boot-arm.h b/arch/arm/include/asm/u-boot-arm.h
index 3a0d0b8..ef4fca6 100644
--- a/arch/arm/include/asm/u-boot-arm.h
+++ b/arch/arm/include/asm/u-boot-arm.h
@@ -47,6 +47,8 @@
 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);
diff --git a/arch/arm/lib/bootm.c b/arch/arm/lib/bootm.c
index eb24222..704849b 100644
--- a/arch/arm/lib/bootm.c
+++ b/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;