Allow getting and setting arch framebuffer config.

Making the fields protected allows them to be set by arch framebuffer
implementations. The getters can be used to retrieve the configuration
from outside the implementation.

src/system/boot/arch/arm/arch_framebuffer.h

@@ -39,12 +39,17 @@ public:
 
 	virtual addr_t			Base() { return fBase; };
 
+			int				Width() { return fCurrentWidth; };
+			int				Height() { return fCurrentHeight; };
+			int				Depth() { return fCurrentDepth; };
+			int				BytesPerRow() { return fCurrentBytesPerRow; };
+
 protected:
 			addr_t			fBase;
-private:
 			int				fCurrentWidth;
 			int				fCurrentHeight;
 			int				fCurrentDepth;
+			int				fCurrentBytesPerRow;
 };