ARM: mach-bcm: disable ftrace in SMC invocation routines

The SMC calling convention uses R7 as an argument register, which
conflicts with its use as a frame pointer when building in Thumb2 mode.
Given that Clang with ftrace does not permit frame pointers to be
disabled, let's omit this compilation unit from ftrace instrumentation.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>

arch/arm/mach-bcm/Makefile

@@ -40,6 +40,7 @@ obj-$(CONFIG_ARCH_BCM_MOBILE_L2_CACHE) += kona_l2_cache.o
 
 # Support for secure monitor traps
 obj-$(CONFIG_ARCH_BCM_MOBILE_SMC) += bcm_kona_smc.o
+CFLAGS_REMOVE_bcm_kona_smc.o += $(CC_FLAGS_FTRACE)
 
 # BCM2835
 ifeq ($(CONFIG_ARCH_BCM2835),y)