bcma: add set/mask macros for 16-bit register access

The BCMA header only had definitions for 32-bit register access. Used
those as a template for the 16-bit flavour. Also changed them to inline
functions to be on the safe side. As offset parameter is used twice there
would be a problem when used like this: bcma_set32(core, offset++, val);

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>