flash/stm32l4x: switch to to c loader instead of assembly loader

flash/stm32l4x: switch to to c loader instead of assembly loader

switching to C loader instead of the assembly version will enhance readability
will reduce the maintenance effort.

besides the switch to C loader, we added a new parameters to the loader
like flash_word_size and flash_sr_bsy_mask in order to support properly
STM32U5x and STM32G0Bx/G0Cx in dual-bank mode.

Change-Id: I24cafc2ba637a065593a0506eae787b21080a0ba
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6109
Tested-by: jenkins
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>