scripts: support quoted sysbuild Kconfig settings in twister

Kconfig settings of string type is passed to CMake with quotes to ensure
they are properly handled, for example when specified in testcase.yml as
>   extra_args:
>    - CONFIG_FOO="bar"

Support sysbuild Kconfig settings `SB_CONFIG` by performing the same
quoting for settings starting with `SB_CONFIG_`.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>