ALSA: emu10k1: added EMU10K1 version of DECLARE_BITMAP macro for UAPI

Fixes userspace compilation error:

error: expected specifier-qualifier-list before ‘DECLARE_BITMAP’
  DECLARE_BITMAP(gpr_valid, 0x200); /* bitmask of valid initializers */

DECLARE_BITMAP macro is not meant for userspace headers and thus
added here as private copy for emu10k.h.

Fix was suggested by Arnd Bergmann <arnd@arndb.de> in message
<2168807.4Yxh5gl11Q@wuerfel> and Takashi Iwai <tiwai@suse.de>
in message <s5h1thx88tk.wl-tiwai@suse.de> on lkml.

Signed-off-by: Mikko Rapeli <mikko.rapeli@iki.fi>
Signed-off-by: Takashi Iwai <tiwai@suse.de>