platform: generic-arm64: Adjust hypervisor_mmio_map_region error handling

On qemu-generic-arm64-gicv3-* builds, hypervisor_mmio_map_region may
unexpectedly return ERR_INVALID_ARGS instead of ERR_NOT_SUPPORTED which
prevents proper UART initialization and blocks console output from the
guest VM. Until this can be root caused, keep going if we get that
error.

Bug: 375584439
Test: Boot trusty in QEMU w/o pvmfw and verify that UART works with
      MMIO_GUARD_ENABLED=true
Change-Id: I89044615eedf4cbd38a45fb058c79af047f6affd

platform/generic-arm64/debug.c

diff --git a/platform/generic-arm64/debug.c b/platform/generic-arm64/debug.c
index 84edf82..9d3885b 100644
--- a/platform/generic-arm64/debug.c
+++ b/platform/generic-arm64/debug.c
@@ -71,9 +71,13 @@
     /*
      * MMIO Guard map UART registers. Ignore not supported which implies that
      * guard is not used.
+     *
+     * TODO: Figure out why we sometimes get ERR_INVALID_ARGS when MMIO Guard is
+     * not supported. It happens on qemu-generic-arm64-gicv3-test-debug builds.
      */
     ret = hypervisor_mmio_map_region(reg_pbase, PAGE_SIZE);
-    if (ret != NO_ERROR && ret != ERR_NOT_SUPPORTED) {
+    if (ret != NO_ERROR && ret != ERR_NOT_SUPPORTED &&
+        ret != ERR_INVALID_ARGS) {
         dprintf(CRITICAL, "failed to mmio guard map uart. error=%d\n", ret);
         return;
     }