Remove the 240MHz CPU config option from sdkconfig.base and create a new
sdkconfig.240mhz file for those boards that want to use 240MHz on boot.
The default CPU frequency is now 160MHz (was 240MHz), to align with the ESP
IDF and support more boards (eg those with D2WD chips).
Fixes issue #5169.
Replaces the `SDKCONFIG` makefile variable with `BOARD`. Defaults to
BOARD=GENERIC. spiram can be enabled with `BOARD=GENERIC_SPIRAM`
Add example definition for TINYPICO, currently identical to GENERIC_SPIRAM
but with custom board/SoC names for the uPy banner.
Seon Rozenblum
Josh Lloyd
Damien George
Jim Mussared