base_hw & omap4: USB HID and framebuffer driver.

Implement 'Signal_receiver::pending()'.

Provide display-subsystem MMIO.

Avoid method ambiguousness in 'Irq_context' in
'dde_linux/src/drivers/usb/signal/irq.cc'
(it derives from two list element classes when using 'base_hw').

Enables demo scenario with 'hw_panda_a2'.

base-hw/include/kernel/syscalls.h

@@ -68,6 +68,7 @@ namespace Kernel
 		NEW_SIGNAL_CONTEXT = 21,
 		AWAIT_SIGNAL = 22,
 		SUBMIT_SIGNAL = 23,
+		SIGNAL_PENDING = 27,
 
 		/* vm specific */
 		NEW_VM = 24,
@@ -465,6 +466,15 @@ namespace Kernel
 	{ syscall(AWAIT_SIGNAL, (Syscall_arg)receiver_id); }
 
 
+	/**
+	 * Get summarized state of all contexts of a signal receiver
+	 *
+	 * \param receiver_id  ID of the targeted receiver kernel-object
+	 */
+	inline bool signal_pending(unsigned long receiver_id) {
+		return syscall(SIGNAL_PENDING, (Syscall_arg)receiver_id); }
+
+
 	/**
 	 * Trigger a specific signal context
 	 *