drivers: staging: dgap: move DG_NAME and DG_PART from "Makefile" to "dgap_driver.h"

Normally, the macros from command line are system specific macros (e.g
__linux, __KERNEL__ ...), and module own macros are usually defined in
their header files.

DG_NAME and DG_PART are driver 'dgap' owned macros which are used by
multiple files within driver, and need be defined in the driver main
header file.

So move DG_NAME and DG_PART to "dgap_driver.h", it not only can make
code clearer, but also can avoid compiling failure when EXTRA_CFLAGS
appended to make command line (e.g. "EXTRA_CFLAGS=-W").

Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>