HAL: Update boundary related HAL functions

This patch contains a couple of updates for boundary HAL:

- For a partition, the boundary is a collection of memory regions,
  hence use a singular number naming instead of plural 'boundaries'.
- As chose 'uintptr_t' as the opaque type for a boundary, the argument
  name should avoid the prefix 'p_' which indicates pointers
  ('p_boundary' changed to 'boundary').
- Change 'pp_boundaries' to 'p_boundary', which is 'pointer of a
  boundary' to indicate it is a boundary container.
- Change the function name 'tfm_hal_update_boundary' to
  'tfm_hal_activate_boundary', as 'update' is not propose-clear.
- Re-ordered the sections in the document for boundary API, and
  updates the function description.

Signed-off-by: Ken Liu <Ken.Liu@arm.com>
Change-Id: Ieee7e497016d1106c395900413bbade5b7b9e79f
22 files changed