drivers: flash: stm32: expose stm32 option byte apis

[fabiobaltieri]

The STM32 flash driver includes some APIs to lock/unlock/set the option bytes. Make these public so that an application can use them to tweak option bytes as needed, add a read api as well.

Allows doing stuff like

        uint32_t val = flash_stm32_option_bytes_read(flash);
        printk("optb=%08x\n", val);

        if (val & FLASH_OPTR_nSWBOOT0_Msk) {
                printk("flip");

                ret = flash_stm32_option_bytes_lock(flash, false);
                if (ret < 0) {
                        printk("unlock failed %d\n", ret);
                        return -1;
                }

                ret = flash_stm32_option_bytes_write(flash, FLASH_OPTR_nSWBOOT0_Msk, 0);
                if (ret < 0) {
                        printk("write failed %d\n", ret);
                        return -1;
                }

                ret = flash_stm32_option_bytes_lock(flash, true);
                if (ret < 0) {
                        printk("lock failed %d\n", ret);
                        return -1;
                }

                printk("done\n");
        }

[erwango]

Thanks @fabiobaltieri.

Looks fine, but however, I wonder if, for consistency sake, these APIs shouldn't be made available through already existing flash_ex_op() api, which is there to expose flash controller specific features ?

Agreed this would be slightly more complex to implement and likely consume more footprint, but I think consistency is key for users.

Alternatively, if there are good reasons not to use flash_ex_op(), let's make it explicit.

[fabiobaltieri]

Looks fine, but however, I wonder if, for consistency sake, these APIs shouldn't be made available through already existing flash_ex_op() api, which is there to expose flash controller specific features ?

Oh that makes load of sense, yeah thanks for the pointer I'll move this back to draft and rework it.