bluenrg-x: simplyfied the driver

bluenrg-x: simplyfied the driver

Adopted only fast algorithm for flash programming:
- write_word and write_byte methods have been removed.
- start and end write alignments have been defined.
Moved flash controller registers offsets in a common file
shared with the flash algorithm.
- the flash base address is passed to the flash algorithm
  as a parameter.
Removed unused functions

Change-Id: I80aeab3994e477044bbcf02e66d9525dae0cb491
Signed-off-by: luca vinci <luca.vinci@st.com>
Reviewed-on: http://openocd.zylin.com/5393
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-by: Michele Sardo <msmttchr@gmail.com>