drivers: flash: Add driver for smartbond

This adds flash driver for Renesas SmartBond(tm) family.

This technically uses QSPI controller but since default and most
commonly used configuration is to boot from external QSPI flash (DA1469x
do not have built-in flash) and that flash is mapped into memory space,
it can be represented as internal flash.

Signed-off-by: Andrzej Kaczmarek <andrzej.kaczmarek@codecoup.pl>
Signed-off-by: Ben Lauret <ben.lauret.wm@renesas.com>