arm64: clean up tools Makefile

Remove unused gen-y.

Remove redundant $(shell ...) because 'mkdir' is done in cmd_gen_cpucaps.

Replace $(filter-out $(PHONY), $^) with the $(real-prereqs) shorthand.

The '&&' in cmd_gen_cpucaps should be replaced with ';' because it is
run under 'set -e' environment.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20220227085232.206529-1-masahiroy@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/tools/Makefile

@@ -5,18 +5,14 @@ kapi := $(gen)/asm
 
 kapi-hdrs-y := $(kapi)/cpucaps.h
 
-targets += $(addprefix ../../../,$(gen-y) $(kapi-hdrs-y))
+targets += $(addprefix ../../../, $(kapi-hdrs-y))
 
 PHONY += kapi
 
-kapi:   $(kapi-hdrs-y) $(gen-y)
-
-# Create output directory if not already present
-_dummy := $(shell [ -d '$(kapi)' ] || mkdir -p '$(kapi)')
+kapi:   $(kapi-hdrs-y)
 
 quiet_cmd_gen_cpucaps = GEN     $@
-      cmd_gen_cpucaps = mkdir -p $(dir $@) && \
-                     $(AWK) -f $(filter-out $(PHONY),$^) > $@
+      cmd_gen_cpucaps = mkdir -p $(dir $@); $(AWK) -f $(real-prereqs) > $@
 
 $(kapi)/cpucaps.h: $(src)/gen-cpucaps.awk $(src)/cpucaps FORCE
 	$(call if_changed,gen_cpucaps)