Fix dangerous casts

On Windows 64-bit, the size of long is 32-bit, thus any pointer to long cast is
not valid. In any case, one should use intptr_t and ptrdiff_t when casting
to integers. This commit attempts to fix all instances reported by GCC.
When relevant, I replaced code by the macros PTR_ADD, ALIGN_UP from system.h

Change-Id: I2273b0e8465d3c4689824717ed5afa5ed238a2dc

firmware/drivers/lcd-16bit.c

@@ -139,7 +139,7 @@ void lcd_hline(int x1, int x2, int y)
         break;
 
       case OPT_COPY:
-        memcpy(dst, (void *)((long)dst + lcd_backdrop_offset),
+        memcpy(dst, PTR_ADD(dst, lcd_backdrop_offset),
                width * sizeof(fb_data));
         break;