target.mk: rework arm architecture level detection

Use kernel config as input instead of -march CFLAGS.
With this change, -march can be dropped and replaced with more specific
optimization flags for better code generation.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

include/target.mk

@@ -259,7 +259,7 @@ ifeq ($(DUMP),1)
     ifneq ($(CONFIG_RTC_CLASS),)
       FEATURES += rtc
     endif
-    FEATURES += $(foreach v,v4 v5 v6 v7,$(if $(filter -march=arm$(v)%,$(CPU_CFLAGS_$(CPU_TYPE))),arm_$(v)))
+    FEATURES += $(foreach v,6 7,$(if $(CONFIG_CPU_V$(v)),arm_v$(v)))
 
     # remove duplicates
     FEATURES:=$(sort $(FEATURES))

target/Config.in

@@ -117,12 +117,6 @@ config armeb
 	select BIG_ENDIAN
 	bool
 
-config arm_v4
-	bool
-
-config arm_v5
-	bool
-
 config arm_v6
 	bool