kselftest/arm64: Validate SVCR in streaming SVE stress test

In the ZA and ZT test programs we explicitly validate that PSTATE.ZA is as
expected on each loop but we do not do the equivalent for our streaming
SVE test, add a check that we are still in streaming mode on every loop
in case that goes wrong.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230922-arm64-ssve-validate-svcr-v1-1-f518960eaeda@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

tools/testing/selftests/arm64/fp/sve-test.S

@@ -473,6 +473,13 @@ function _start
 //	mov	x8, #__NR_sched_yield	// Encourage preemption
 //	svc	#0
 
+#ifdef SSVE
+	mrs	x0, S3_3_C4_C2_2	// SVCR should have ZA=0,SM=1
+	and	x1, x0, #3
+	cmp	x1, #1
+	b.ne	svcr_barf
+#endif
+
 	mov	x21, #0
 0:	mov	x0, x21
 	bl	check_zreg
@@ -553,3 +560,15 @@ function vl_barf
 	mov	x1, #1
 	svc	#0
 endfunction
+
+function svcr_barf
+	mov	x10, x0
+
+	puts	"Bad SVCR: "
+	mov	x0, x10
+	bl	putdecn
+
+	mov	x8, #__NR_exit
+	mov	x1, #1
+	svc	#0
+endfunction