iwlwifi: move iwl4965_get_dma_hi_address function to iwl-helpers.h

This patch moves iwl4965_get_dma_hi_address function to iwl-headers.h
as iwl_get_dma_hi_address. This function will be used in more chipsets
than only 4965.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>