kern, arm: Dump dmesg on kernel panic/oops

Add helper functions to dump the guest kernel's dmesg buffer to a text
file in m5out. This functionality is split into two parts. First, a
dmesg dump function that can be used in other places:

void Linux::dumpDmesg(ThreadContext *, std::ostream &)

This function is used to implement two PCEvents: DmesgDumpEvent and
KernelPanic event. The only difference between the two is that the
latter produces a gem5 panic instead of a warning in addition to
dumping the kernel log.

Change-Id: I6d2af1d666ace57124089648ea906f6c787ac63c
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Gabor Dozsa <gabor.dozsa@arm.com>

src/arch/arm/ArmSystem.py

@@ -98,6 +98,14 @@ class LinuxArmSystem(GenericArmSystem):
     type = 'LinuxArmSystem'
     cxx_header = "arch/arm/linux/system.hh"
 
+    @classmethod
+    def export_method_cxx_predecls(cls, code):
+        code('#include "arch/arm/linux/system.hh"')
+
+    @classmethod
+    def export_methods(cls, code):
+        code('''void dumpDmesg();''')
+
 class FreebsdArmSystem(GenericArmSystem):
     type = 'FreebsdArmSystem'
     cxx_header = "arch/arm/freebsd/system.hh"