ARM: 9313/1: vdso: add missing prototypes

The __vdso_clock_* functions have no prototype, and the
__eabi_unwind_cpp_pr* functions have a prototype in a header that is
not included before the definition:

arch/arm/vdso/vgettimeofday.c:10:5: error: no previous prototype for '__vdso_clock_gettime' [-Werror=missing-prototypes]
arch/arm/vdso/vgettimeofday.c:16:5: error: no previous prototype for '__vdso_clock_gettime64' [-Werror=missing-prototypes]
arch/arm/vdso/vgettimeofday.c:22:5: error: no previous prototype for '__vdso_gettimeofday' [-Werror=missing-prototypes]
arch/arm/vdso/vgettimeofday.c:28:5: error: no previous prototype for '__vdso_clock_getres' [-Werror=missing-prototypes]
arch/arm/vdso/vgettimeofday.c:36:6: error: no previous prototype for '__aeabi_unwind_cpp_pr0' [-Werror=missing-prototypes]
arch/arm/vdso/vgettimeofday.c:40:6: error: no previous prototype for '__aeabi_unwind_cpp_pr1' [-Werror=missing-prototypes]
arch/arm/vdso/vgettimeofday.c:44:6: error: no previous prototype for '__aeabi_unwind_cpp_pr2' [-Werror=missing-prototypes]

Add the prototypes in an appropriate header and ensure that
both are included here.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>