debug/gdb: add gdb 7.8

Add updated gdb 7.8 to the available versions of gdb.

Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>
debug/gdb: add GDB_HAS_PYTHON

Add a Kconfig boolean to enable python, only if GDB_7_0_or_later.

Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>