Update docs and tests for ARM gdb support

Updated docs to now show arm is supported.
Updated the build test to run on aarch

Author: JackThomson2

docs/gdb-debugging.md

@@ -2,7 +2,7 @@
 
 Firecracker supports debugging the guest kernel via GDB remote serial protocol.
 This allows us to connect GDB to the firecracker process and step through debug
-the guest kernel. Currently only debugging on x86 is supported.
+the guest kernel.
 
 The GDB feature requires Firecracker to be booted with a config file.
 

tests/integration_tests/build/test_gdb.py

@@ -12,7 +12,6 @@
 TARGET = "{}-unknown-linux-musl".format(MACHINE)
 
 
-@pytest.mark.skipif(MACHINE != "x86_64", reason="GDB runs only on x86_64.")
 def test_gdb_compiles():
     """Checks that Firecracker compiles with GDB enabled"""