dts: mspm0: Fix timer/counter/pwm names to enforce uniqueness

There are 14 TIMG and 2 TIMA, all which can be either a counter or a pwm,
so let's fix the names to avoid ambiguity and enforce uniqueness.

Rule applied here being:

tim<g/a><n>: tim<g/a><n>@<address> {
        ...

        counter<g/a><n>: counter<g/a><n> {
                ...
        };

        pwm<g/a><n>: pwm<g/a><n> {
                ...
        };
};

It will be much easier then once get the 16 timer nodes included.

Signed-off-by: Tomasz Bursztyka <tobu@bang-olufsen.dk>