Make camera mount and solo gimbal board configured features

[andyp1per]

This PR saves a ton of flash:

• Turn the camera mount into a board level feature controlled by HAL_MOUNT_ENABLED
• Turn the solo gimbal into a board feature controlled by HAL_SOLO_GIMBAL_ENABLED (props for the name!)
• disable the camera mount on mini boards - the intersection of mini board builds and gimbals has got to be close to zero
• disable the solo gimbal on kakute and omnibus 1mB boards - against users close to zero (could do this for all 1mb boards)

Saves 18k flash on the 1mB boards
Saves 24k flash on the mini boards

[khancyr]

I love this !

[tridge]

just a small change to make solo gimbal off by default, and enabled on 2M boards

[Pedals2Paddles]

So this looks like it is enabled by default and disabled in hwdef where specifically not wanted? Would it be even better to disable the solo gimbal by default, requiring it to be enabled in the hwdef? That can be enabled for the solo's build target hwdef files only. And not exist in all the rest that don't need it.

[andyp1per]

@Pedals2Paddles it's disabled by default on all 1Mb boards - see AP_Mount.h

[Pedals2Paddles]

I see where it's disabled on the 1MB boards. I'm not seeing where it is actually defined as enabled to begin with? I'm actually suggesting we save the flash space on all boards by only enabling the Solo gimbal in the hwdef files for the build targets for the Solo.

[andyp1per]

It's enabled on 2MB boards in AP_Mount.h. But happy to disable everywhere if you can give me the list where it should be enabled?

[hdtechk]

Just a comment here I have a copter that is not a solo that has a solo gimbal installed. I personally would like to see it stay on 2M boards