cmake: remove platform / build file specific escaping

Fixes: #41435

Remove build host specific escaping of start symbol command argument.
The start symbol for armlink is: Image$$device$$Base
and were escaped as: Image\\$$\\$$device\\$$\\$$Base

However, the $ must only be escaped in Linux and MacOS, not on windows
hosts.

Instead of escaping the start symbol in the CMake code then it is better
to use the VERBATIM flag on `add_custom_command()` which ensures correct
escaping for the build host.

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