flash/nor/stmqspi: Replace macros with static inline functions

There is no good reason to use macros instead of static inline functions. The
current code is hard maintain. For example, it changes variables outside of the
macro scope. Also, it is conflicting with the C coding style.

Change-Id: I5ac9d2ae076ef73c176d4e32b2e7e0a99fa875ab
Signed-off-by: Marc Schink <dev@zapb.de>
Reviewed-on: http://openocd.zylin.com/6046
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>