target-arm: Implement AArch64 OSLAR/OSLSR_EL1 sysregs

Added oslar_write function to OSLAR_EL1 sysreg, using a status variable
in ARMCPUState.cp15 struct (oslsr_el1). This variable is also linked
to the newly added read-only OSLSR_EL1 register.

Linux reads from this register during its suspend/resume procedure.

Signed-off-by: Davorin Mista <davorin.mista@aggios.com>
[PMM: folded a long line and tweaked a comment]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index 5fb0479..d1b5bc1 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -379,6 +379,7 @@
         uint64_t dbgwvr[16]; /* watchpoint value registers */
         uint64_t dbgwcr[16]; /* watchpoint control registers */
         uint64_t mdscr_el1;
+        uint64_t oslsr_el1; /* OS Lock Status */
         /* If the counter is enabled, this stores the last time the counter
          * was reset. Otherwise it stores the counter value
          */