target: fix unaligned return of target_get_working_area_avail()

target: fix unaligned return of target_get_working_area_avail()

The working area allocation routines use 4 byte word alignment.
In the corner case the size of the working area is not aligned,
target_alloc_working_area() of size = target_get_working_area_avail()
will fail because the size gets aligned up and does not fit to the area
which size is aligned down.

Align down the result of target_get_working_area_avail() to cope with that
corner case.

While on it use fancy ALIGN_... macros instead of bitwise and operator.

Change-Id: Ia2a1e861c401c2c78fe6323379a3776fb4f47b06
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/7096
Tested-by: jenkins
Reviewed-by: Erhan Kurubas <erhan.kurubas@espressif.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>