target/ppc: Allow PIR read in privileged mode

According to PowerISA, the PIR register should be readable in privileged
mode also, not only in hypervisor privileged mode.

PowerISA 3.0 - 4.3.3 Processor Identification Register

"Read access to the PIR is privileged; write access is not provided."

Figure 18 in section 4.4.4 explicitly confirms that mfspr PIR is privileged
and doesn't require hypervisor state.

Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Alexander Graf <agraf@suse.de>
Cc: qemu-ppc@nongnu.org
Signed-off-by: Leandro Lupori <leandro.lupori@gmail.com>
Reviewed-by: Jose Ricardo Ziviani <joserz@linux.ibm.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

target/ppc/translate_init.inc.c

@@ -7819,7 +7819,7 @@ static void gen_spr_book3s_ids(CPUPPCState *env)
     /* Processor identification */
     spr_register_hv(env, SPR_PIR, "PIR",
                  SPR_NOACCESS, SPR_NOACCESS,
-                 SPR_NOACCESS, SPR_NOACCESS,
+                 &spr_read_generic, SPR_NOACCESS,
                  &spr_read_generic, NULL,
                  0x00000000);
     spr_register_hv(env, SPR_HID0, "HID0",