staging: easycap: remove redunant headers

place all globals to easycap.h, which is included
by all c-files
easycap_standard: fix declaration vs. definiton conflict

Cc: Mike Thomas <rmthomas@sciolus.org>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>