cpu/$(CPU)/Makefile.features and cpu/$(CPU)/Makefile.dep are
automatically included
Part of moving CPU/CPU_MODEL definition to Makefile.features to have it
available before Makefile.include.
The board should process its CPU features.
This has the consequence to make 'periph_pm' visible to the board.
I also removed the duplicate FEATURES_PROVIDED from the board defined in
the cpu.
Remove duplicate handling of `periph_rtc` dependency to `periph_rtt` now
declared in the cpu.
Also the makefiles should not parse FEATURES_REQUIRED as it does not
guarantee anything as features could also be requested by FEATURES_OPTIONAL.
In practice it should parse it using `USEMODULE`.
Added HiFive1 to BOARD_INSUFFICIENT_MEMORY list for examples and tests that are too big to fit
build: fixed missing syscall and cpuid failures
Added missing syscall stubs for nanostubs and fixed compile error with cpuid periph
build: fixed whitespace error
build: add hifive1 to more BOARD_INSUFFICIENT_MEMORY
doc: fixed doxygen warnings
Addressed Doxygen warnings in source file comments
doc: more doxygen fixes
doc: even more doxygen fixes
doc: more changes
build: fix pedantic and rdci_simple build failures
make: exclude lua
