nordic: Use hal/ in all inclusions of nrfx HAL header files

Header files of nrfx HALs are not supposed to be included directly
but only with their names prepended with the hal/ directory (so that
an inclusion of an nrfx HAL header clearly differs from an inclusion
of an nrfx driver header).

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>