script: west_commands: core: Add --reset-type parameter

For some devices, the default JLink reset type may not work properly, so
allow overriding the reset type by passing, e.g. --reset-type=12 when
flashing.

Add new field to RunnerCaps to allow runners to specify either a fixed
list of possible types, or True to expose the standard --reset-type
parameter for that runner.

Signed-off-by: Pete Johanson <pete.johanson@analog.com>