Makefile: Optimize for sm8150's Kryo 485 CPU setup

The big (Gold and Prime) cores are derived from ARM's Cortex-A75
reference design, while the little (Silver) cores are derived from
Cortex-A55.

Clang doen't support optimizing for two clusters at once, so help the
weaker little cluster out a bit by optimizing exclusive for it instead
since it needs all the speed it can get.

Test: GCC 9.1.0 and Clang 10.0.0svn both compile working kernels
Signed-off-by: Danny Lin <danny@kdrag0n.dev>

Makefile

@@ -682,6 +682,12 @@ ifdef CONFIG_PROFILE_ALL_BRANCHES
 KBUILD_CFLAGS	+= -O2 $(call cc-disable-warning,maybe-uninitialized,)
 else
 KBUILD_CFLAGS   += -O2
+ifeq ($(cc-name),gcc)
+KBUILD_CFLAGS	+= -mcpu=cortex-a76.cortex-a55 -mtune=cortex-a76.cortex-a55
+endif
+ifeq ($(cc-name),clang)
+KBUILD_CFLAGS	+= -mcpu=cortex-a55 -mtune=cortex-a55
+endif
 endif
 endif