semihosting: move semihosting tests to multiarch

It may be arm-compat-semihosting but more than one architecture uses
it so lets move the tests into the multiarch area. We gate it on the
feature and split the semicall.h header between the arches.

Also clean-up a bit of the Makefile messing about to one common set of
runners.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210323165308.15244-6-alex.bennee@linaro.org>

tests/tcg/aarch64/semicall.h

@@ -0,0 +1,18 @@
+/*
+ * Semihosting Tests - AArch64 helper
+ *
+ * Copyright (c) 2019
+ * Written by Alex Bennée <alex.bennee@linaro.org>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+uintptr_t __semi_call(uintptr_t type, uintptr_t arg0)
+{
+    register uintptr_t t asm("x0") = type;
+    register uintptr_t a0 asm("x1") = arg0;
+    asm("hlt 0xf000"
+        : "=r" (t)
+        : "r" (t), "r" (a0));
+    return t;
+}