tools - Generate valid embedded newlines in strings

* Use the posix string concat instead of actually escaping
a hard newline inside the string.

This is not legal in C any more (it used to be,

tools - Generate valid embedded newlines in strings

* Use the posix string concat instead of actually escaping
a hard newline inside the string.

This is not legal in C any more (it used to be, ages ago):

"abc\
def"

Instead we have to use:

"abc\n"
"def"

* Fixes the awk scripts to generate valid C strings.

Reported-by: zrj

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fw_stub.awk: correct usage message

* Add information about optional version and parent for the firmware
image.

* Show that the -m option is mandatory.

fw_stub.awk: fix processing of values for the options when separated by space