audio: split IN_T into two separate constants

audio: split IN_T into two separate constants

Split IN_T into BSIZE and ITYPE, to avoid expansion if the OS has
defined macros for the intX_t and uintX_t types. The IN_T constant is
then defined in mixeng_template.h so it can be used by the
functions/macros on this header file.

This change has been tested successfully under Debian Linux and NetBSD
6.0BETA.

Cc: Vassili Karpov (malc) <av1474@comtv.ru>
Signed-off-by: Roger Pau Monne <roger.pau@citrix.com>
Signed-off-by: malc <av1474@comtv.ru>