platform: nordic_nrf: Update serial IRQ naming according to name change

Update serial IRQ naming to match the IRQ naming change introduced in
the nordic MDK.
Since the startup files wasn't updated to declare the interrupt vectors
with the old name the name change redifinion in
nrf5340_application_name_change caused the interrupt handler to not be
defined.

Change-Id: Iab2ada4381164efb9b29a51dd6e7852e564e91c8
Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>
6 files changed