The file always exist so no need to do '-include'.

Replaced using:

    sed -i 's|-\(include $(RIOTCPU)/.*/Makefile.features\)|\1|' \
        $(git grep -l  '$(RIOTCPU)/.*/Makefile.features' boards)

Includes of $(CPU)/include and $(BOARD)/include and already added in the
main Makefile.include.

Verification:

There are no common headers names between boards and cpus.
Except native that has a 'periph_conf.h' in cpu instead of being in board.

- replace brief with name where required
- remove some unwanted empty lines
- fix missing closing doxygen name block

In CPU definitions we should not be explicilty naming peripheral modules to use
via USEMODULE (one should use FEATURES_PROVIDED instead).
Plus add missing cpu_init() and periph_init() methods.
This commit removes periph_hwrng support from the pic32mx cpu builds as
pic32mx does not have hwrng only pic32mz does.

Signed-off-by: Francois Berder <fberder@outlook.fr>

Signed-off-by: Francois Berder <fberder@outlook.fr>

U3RXREG is the RX buffer for UART3. U3RXR is the register for
controlling the input pin for UART3.

Signed-off-by: Francois Berder <francois.berder@imgtec.com>

Signed-off-by: Francois Berder <francois.berder@imgtec.com>

Signed-off-by: Francois Berder <francois.berder@imgtec.com>

This board features a pic32mx470f512h PIC32 device with a MIPS core.