HAL_AVR: switched to 8 bit mask

max buffer size is now 256. This makes serial faster
HAL_SMACCM: fixed build warning
AP_Baro: only build BMP085 driver on APM1
AP_InertialSensor: only build Oilpan driver on APM1
AP_GPS: put SIRF init_messages in progmem

this saves 32 bytes of memory
MAVLink: moved CRC table into program

this saves 256 bytes of memory
HAL_AVR: make Console a direct wrapper of uartA

this saves a bunch of memory, and we don't really need separate
console support on AVR
Copter: move memcheck_init() earlier in setup
Plane: move memcheck_init() earlier in setup()
Copter: tweak the serial buffer sizes

we only need the large buffers for HIL
HAL_AVR: ensure we can handle a 256 size buffer
HAL_AVR: tweak the default serial buffer sizes

this reduces memory fragmentation a lot, saving memory