scripts/gdb: fix issue with dmesg.py and python 3.X

scripts/gdb: fix issue with dmesg.py and python 3.X

When built against Python 3, GDB differs in the return type for its
read_memory function, causing the lx-dmesg command to fail.

Now that we have an improved read_16() we can use the new
read_memoryview() abstraction to make lx-dmesg return valid data on both
current Python APIs

Tested with python 3.4 and 2.7
Tested with gdb 7.7

Link: http://lkml.kernel.org/r/28477b727ff7fe3101fd4e426060e8a68317a639.1462865983.git.jan.kiszka@siemens.com
Signed-off-by: Dom Cote <buzdelabuz2+git@gmail.com>
[kieran@bingham.xyz: Adjusted commit log to better reflect code changes]
Tested-by: Kieran Bingham <kieran@bingham.xyz> (Py2.7,Py3.4,GDB10)
Signed-off-by: Kieran Bingham <kieran@bingham.xyz>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>