scripts/gdb: fix lx-timerlist for Python3

scripts/gdb: fix lx-timerlist for Python3

Below incompatibilities between Python2 and Python3 made lx-timerlist fail
to run under Python3.

o xrange() is replaced by range() in Python3
o bytes and str are different types in Python3
o the return value of Inferior.read_memory() is memoryview object in
  Python3

akpm: cc stable so that older kernels are properly debuggable under newer
Python.

Link: https://lkml.kernel.org/r/TYCP286MB2146EE1180A4D5176CBA8AB2C6819@TYCP286MB2146.JPNP286.PROD.OUTLOOK.COM
Signed-off-by: Peng Liu <liupeng17@lenovo.com>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>