boards: hifive_unleashed: add support for E51 and U54 targets

Add `hifive_unleashed//e51` (earlier selected by default, using
`hifive_unleashed`) and `hifive_unleashed//u54` targets.

Define work-area for other 4 cores in openocd.cfg

Update twister platform white/black lists, to support new targets

Signed-off-by: Jakub Wasilewski <jwasilewski@internships.antmicro.com>
Signed-off-by: Filip Kokosinski <fkokosinski@antmicro.com>

tests/drivers/console/line_splitting/testcase.yaml

@@ -2,7 +2,7 @@ common:
   tags:
     - drivers
     - console
-  platform_allow: hifive1 hifive_unleashed
+  platform_allow: hifive1 hifive_unleashed/fu540/e51
   harness: robot
 
 tests:

tests/subsys/zbus/integration/testcase.yaml

@@ -3,7 +3,8 @@ tests:
     platform_exclude:
       - m2gl025_miv
       - qemu_cortex_a9
-      - hifive_unleashed
+      - hifive_unleashed/fu540/e51
+      - hifive_unleashed/fu540/u54
       - fvp_base_revc_2xaemv8a/fvp_base_revc_2xaemv8a/smp/ns
     tags: zbus
     integration_platforms: