Avoid duplicate definition of I810CopyROP in i810.h and i810_accel.c, fixes...

Avoid duplicate definition of I810CopyROP in i810.h and i810_accel.c, fixes compilation with -fno-common/gcc-10.

The global variable I810CopyROP was defined twice, remove it from i810.h (it's still declared as "extern" there, which is the correct way to use a global in multiple files). Such code was accepted by previous versions of gcc, however it's not correct and future gcc versions (10+) will reject it. In older gcc versions this stricter behavior can be enforced with the flag -fno-common.