implement getWidth4FB_HW_ACC in fb_accel class

This helper to determine alignment for hardware blitting is now in
system/helpers.h, where it does not really belong. Put it into the
framebuffer class instead. Framebuffers that don't need it will just
get a dummy function, the cs_hd2 framebuffer gets the real thing.
Also add a bool function that indicates the need for alignment.


Origin commit data
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Commit: 05d1732cea
Author: Stefan Seyfried <seife@tuxbox-git.slipkontur.de>
Date: 2017-02-14 (Tue, 14 Feb 2017)

src/driver/fb_generic.h

@@ -185,6 +185,8 @@ class CFrameBuffer : public sigc::trackable
 		bool getActive() const;                     // is framebuffer active?
 		void setActive(bool enable);                     // is framebuffer active?
 		virtual void setupGXA() { return; };             // reinitialize stuff
+		virtual bool needAlign4Blit() { return false; };
+		virtual uint32_t getWidth4FB_HW_ACC(const uint32_t x, const uint32_t w, const bool max=true);
 
 		void setTransparency( int tr = 0 );
 		virtual void setBlendMode(uint8_t mode = 1);