wma: Store ASF header info in afhi->techinfo.

wma: Store ASF header info in afhi->techinfo.

This changes the wma audio format handler and decoder to store
the ASF header bits we care about (exp_vlc, bit reservoir, and
variable block length) in struct asf_header_info instead of struct
private_wmadec_data.

This way the wma audio format handler can print this information in
its ->techinfo string for the audio file.