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/drivers.c

@@ -66,7 +66,7 @@ static const struct flash_driver * const flash_drivers[] = {
 	&psoc6_flash,
 	&qn908x_flash,
 	&renesas_rpchf_flash,
-	&rp2040_flash,
+	&rp2xxx_flash,
 	&sh_qspi_flash,
 	&sim3x_flash,
 	&stellaris_flash,