oeqa/systemd_boot: Ensure ssh-pregen-hostkeys are available for the test

Since ssh-pregen-hostkeys is now restricted to qemu machines, add in configuration
allowing it to become available for this test on genericx86-64.

(From meta-yocto rev: b65a1e39dea6d215221f400709f7f3f4c110a948)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-yocto-bsp/lib/oeqa/selftest/cases/systemd_boot.py

@@ -18,7 +18,8 @@ class Systemdboot(OESelftestTestCase):
 
         # Set EFI_PROVIDER = "systemdboot" and MACHINE = "genericx86-64" in conf/local.conf
         features = 'EFI_PROVIDER = "systemd-boot"\n'
-        features += 'MACHINE = "genericx86-64"'
+        features += 'MACHINE = "genericx86-64"\n'
+        features += 'COMPATIBLE_MACHINE:pn-ssh-pregen-hostkeys:genericx86-64 = "genericx86-64"\n'
         self.append_config(features)
 
         image = 'core-image-minimal'