fix compile warnings for gcc 6.2.0

Most of issues discovered by gcc 6.2.0 are:
warning: implicit declaration of function '...'
which make sense since this functions was never declared,
espesially functions provided by ROM.

In the last case, correct usage of this functions was never
checked by compiler.

So, wellcome in to GCC 6.2.0 age ;)

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>