arm: Add support for memory-mapped m5ops

Add support for a memory mapped m5op interface. When enabled, the TLB
intercepts accesses in the 64KiB region designated by the
ArmTLB.m5ops_base parameter. An access to this range maps to a
specific m5op call. The upper 8 bits of the offset into the range
denote the m5op function to call and the lower 8 bits denote the
subfunction.

Change-Id: I55fd8ac1afef4c3cc423b973870c9fe600a843a2
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2964

src/arch/arm/ArmSystem.py

@@ -76,6 +76,10 @@ class ArmSystem(System):
     have_large_asid_64 = Param.Bool(False,
         "True if ASID is 16 bits in AArch64 (ARMv8)")
 
+    m5ops_base = Param.Addr(0,
+        "Base of the 64KiB PA range used for memory-mapped m5ops. Set to 0 "
+        "to disable.")
+
 class GenericArmSystem(ArmSystem):
     type = 'GenericArmSystem'
     cxx_header = "arch/arm/system.hh"