tests/tcg/s390x: Add PSW modification tests

Add several small tests that check the PSW modification instructions:

* lpsw.S checks whether LPSW works correctly in the "happy" case.

* lpswe-early.S checks whether early exceptions are recognized and
  whether the correct ILC and old PSW are stored when they happen.

* ssm-early.S, stosm-early.S and exrl-ssm-early.S check the special
  handling of SSM and STOSM with respect to early exceptions.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230315020408.384766-4-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/tcg/s390x/lpsw.S

@@ -0,0 +1,36 @@
+/*
+ * Test the LPSW instruction.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+    .org 0x140
+svc_old_psw:
+    .org 0x1c0                         /* supervisor call new PSW */
+    .quad 0x80000000,svc               /* 31-bit mode */
+    .org 0x200                         /* lowcore padding */
+
+    .globl _start
+_start:
+    lpsw short_psw
+lpsw_target:
+    svc 0
+expected_pswa:
+    j failure
+
+svc:
+    clc svc_old_psw(16),expected_psw   /* correct full PSW? */
+    jne failure
+    lpswe success_psw
+failure:
+    lpswe failure_psw
+
+    .align 8
+short_psw:
+    .long 0x90001,0x80000000+lpsw_target         /* problem state,
+                                                    64-bit mode */
+expected_psw:
+    .quad 0x1000180000000,expected_pswa          /* corresponds to short_psw */
+success_psw:
+    .quad 0x2000000000000,0xfff        /* see is_special_wait_psw() */
+failure_psw:
+    .quad 0x2000000000000,0            /* disabled wait */