Expand the frequency range of vtx

[qubicllj]

There are 1.2, 2.4, 3.3, 4.9 GHz vtx on the market, i think it is necessary to expand the minimum frequency to 1000 MHz .

ImmersionRC Rapidfire vrx support up to 6100 MHz , Some TrueRC antennas support up to 6.7 GHz, so i recommend expand the maximum frequency to 6700 MHz .

[github-actions]

Do you want to test this code? You can flash it directly from Betaflight Configurator:

• Simply put #13530 (this pull request number) in the Select commit field of the Configurator firmware flasher tab (you need to Enable expert mode, Show release candidates and Development).

WARNING: It may be unstable. Use only for testing!

[ledvinap]

This should be improved, but not by changing constants.

VTX_SETTINGS_MAX_FREQUENCY_MHZ seems to be main source of limits, so it should be used where possible. Then it wou mean changing single constant.

Also, it will expand possible range 5x ... is that handled ergonomically in OSD ?

[nerdCopter]

Betaflight will only allow "Legal" ranges. I don't know all the ranges for all the countries. I believe "Legal" means "Hobby" ranges. I am not an authority, however.
If the legal ranges are separated (gapped), then another solution will be required.