test: posix: xsi_realtime: do not exclude intel_ish platforms

Previously, intel_ish platforms would fail to link due to
missing `arch_mem_map()` and `arch_mem_unmap()` symbols due
to nuances in the x86 architecture on those platforms.

A separate commit has made MMU a non-user-configurable option,
which removes the ambiguity in POSIX.

Signed-off-by: Chris Friedt <[email protected]>
(cherry picked from commit 784f5b5)

Author: cfriedt

tests/posix/xsi_realtime/testcase.yaml

@@ -13,10 +13,6 @@ common:
   platform_exclude:
     # linker_zephyr_pre0.cmd:140: syntax error (??)
     - qemu_xtensa/dc233c
-    # CONFIG_MMU=y but no arch_mem_map() or arch_mem_unmap()
-    - intel_ish_5_4_1
-    - intel_ish_5_6_0
-    - intel_ish_5_8_0
     - native_sim
     - native_sim/native/64
 tests: