ext: Atmel ASF: remove unused and broken preprocesor macros

Header files from Atmel ASF define several preprocesor macros
which are unused and break compilation with some toolchains.
This patch removes those macros. Currently only from same70q21.h
header file which is used by SAM E70 Xplained target board.

Jira: ZEP-976
Change-Id: I13adb92c73773815c6df221ef33b0f56795f1d8c
Signed-off-by: Piotr Mienkowski <piotr.mienkowski@gmail.com>