flash/stm32l4x: fix flash programming in 64-bit hosts

flash/stm32l4x: fix flash programming in 64-bit hosts

stm32l4_work_area struct is shared between the loader and stm32l4x flash driver

'*wp' and '*rp' pointers' size is 4 bytes each since stm32l4x devices have
32-bit processors.

however when used in openocd code, their size depends on the host
  if the host is 32-bit, then the size is 4 bytes each.
  if the host is 64-bit, then the size is 8 bytes each.

to avoid this size difference, change their types depending on the
usage (pointers for the loader, and 32-bit integers in openocd code).

Change-Id: I0a3df4bb4bf872b01cdb9357eb28307868d7d469
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6556
Tested-by: jenkins
Reviewed-by: Yestin Sun <sunyi0804@gmail.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>