MAIN_PLECO_V2

ChibiOS: Upgrade to latest 3.0 version (unstable).

MAIN_PLECO_V1

build: Increase PORT_INT_REQUIRED_STACK.

PORT_INT_REQUIRED_STACK defaults to 64 bytes on ARMv7 with
ChibiOS 3.0 with a comment that it is set conservatively to have
space for stack frames etc. with compiler optimisations disabled.

Increase PORT_INT_REQUIRED_STACK even further to avoid stack
overflows with all optimisations off and debug checks on.

MAIN_FPS_V1

compile-all: Query core count instead of -j4.