loader: unload command should reset tg_kernel_supported in gfx_state

While loading kernel, we check if vt/vbe backend support is included in
kernel and set the tg_kernel_supported flag in gfx_state. unload
command needs to reset this flag to allow next load to perform
this check with new kernel.

Reported by: jhb

stand/common/module.c

@@ -271,6 +271,8 @@ unload(void)
 	}
 	loadaddr = 0;
 	unsetenv("kernelname");
+	/* Reset tg_kernel_supported to allow next load to check it again. */
+	gfx_state.tg_kernel_supported = false;
 }
 
 COMMAND_SET(unload, "unload", "unload all modules", command_unload);