flash/nor/rp2040: refactoring: change rp2040 to rp2xxx

While on it use calloc() instead of malloc()/memset()
Drop useless implementation of rp2040_flash_free_driver_priv()
- exactly same as default_flash_free_driver_priv()
Code style fixes forced by checkpatch

Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Change-Id: I5c56c4a7d586c0dcab164a45e8f6200ea9a3bd1d
Reviewed-on: https://review.openocd.org/c/openocd/+/8455
Tested-by: jenkins

src/flash/nor/Makefile.am

@@ -59,7 +59,7 @@ NOR_DRIVERS = \
 	%D%/psoc6.c \
 	%D%/qn908x.c \
 	%D%/renesas_rpchf.c \
-	%D%/rp2040.c \
+	%D%/rp2xxx.c \
 	%D%/rsl10.c \
 	%D%/sfdp.c \
 	%D%/sh_qspi.c \