sh: Fix DSP opcode regression for SH3-DSP parts.

Older versions of binutils do not support -Wa,-isa= tuning, which is
something we rely on for enabling DSP opcode support on the newer
parts. SH3-DSP parts can still be handled with -Wa,-dsp even if the
newer parts require the newer versions of binutils for supporting the
new opcodes.

This was broken in -rc1 when the SH4AL-DSP support was being reworked,
and is needed to get SH3-DSP working with older toolchains again.
Reported-by: Markus Brunner <super.firetwister@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/Makefile

@@ -34,6 +34,8 @@ isa-y			:= $(isa-y)-nofpu
 endif
 endif
 
+isa-y			:= $(isa-y)-up
+
 cflags-$(CONFIG_CPU_SH2)		:= $(call cc-option,-m2,)
 cflags-$(CONFIG_CPU_SH2A)		+= $(call cc-option,-m2a,) \
 					   $(call cc-option,-m2a-nofpu,)
@@ -46,7 +48,20 @@ cflags-$(CONFIG_CPU_SH4A)		+= $(call cc-option,-m4a,) \
 cflags-$(CONFIG_CPU_BIG_ENDIAN)		+= -mb
 cflags-$(CONFIG_CPU_LITTLE_ENDIAN)	+= -ml
 
-cflags-y	+= $(call as-option,-Wa$(comma)-isa=$(isa-y),) -ffreestanding
+#
+# -Wa,-isa= tuning implies -Wa,-dsp for the versions of binutils that
+# support it, while -Wa,-dsp by itself limits the range of usable opcodes
+# on certain CPU subtypes. Try the ISA variant first, and if that fails,
+# fall back on -Wa,-dsp for the old binutils versions. Even without DSP
+# opcodes, we always want the best ISA tuning the version of binutils
+# will provide.
+#
+isaflags-y	:= $(call as-option,-Wa$(comma)-isa=$(isa-y),)
+
+isaflags-$(CONFIG_SH_DSP)		:= \
+	$(call as-option,-Wa$(comma)-isa=$(isa-y),-Wa$(comma)-dsp)
+
+cflags-y	+= $(isaflags-y) -ffreestanding
 
 cflags-$(CONFIG_MORE_COMPILE_OPTIONS)	+= \
 	$(shell echo $(CONFIG_COMPILE_OPTIONS) | sed -e 's/"//g')