flash/nor: add DesignWare SPI controller driver

Driver for DesignWare SPI controller, found on many SoCs (see compatible
list in Linux device tree bindings
Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.yaml). This
implementation only supports MIPS as it was the only one available for the
tests, however, adding support for other architectures should require only
few adjustments. Driver relies on flash/nor/spi.h to find Flash chip info.
Driver internal functions support 24bit addressing mode, but due to
limitations of flash/nor/spi.h, it is not used. The reported writing speed
is about 60kb/s.
Lint, sanitizer and valgrind reported warnings were not related to the
driver.

Change-Id: Id3df5626ab88055f034f74f274823051dedefeb1
Signed-off-by: Sergey Matsievskiy <matsievskiysv@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8400
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/flash/nor/Makefile.am

@@ -26,6 +26,7 @@ NOR_DRIVERS = \
 	%D%/cc26xx.c \
 	%D%/cfi.c \
 	%D%/dsp5680xx_flash.c \
+	%D%/dw-spi.c \
 	%D%/efm32.c \
 	%D%/em357.c \
 	%D%/eneispif.c \
@@ -89,6 +90,7 @@ NORHEADERS = \
 	%D%/cc26xx.h \
 	%D%/cfi.h \
 	%D%/driver.h \
+	%D%/dw-spi-helper.h \
 	%D%/imp.h \
 	%D%/non_cfi.h \
 	%D%/ocl.h \