Updated Serial Flash interface & Network buffer classes to avoid warnings and improve robustness. Fixed issue with mbed_overrides trying to use an old implementation of cy_serial_flash_init() function.
This avoids a stack overflow if sleep is called for the first time from
the idle thread (which by default has a fairly small stack, and which is
already fairly deep by the time it calls into the usticker adapter)
Purposes:
* Remove MbedOS-specific code from system_psoc6_{cm4,cm0plus}.c
to simplify updates to new PDL version (startup code is part of PDL).
* Unify mbed_sdk_init initialization sequence for both CPU cores.
This change is non-functional, sequence itself is not changed for any
of the PSoC 6 M4/M0 PSA/non-PSA targets.