[AArch64][SVE 12/32] Make more use of bfd_boolean
    
    Following on from the previous patch, which converted the
    aarch64_reg_parse_32_64 parameters to bfd_booleans, this one
    does the same for parse_address_main and parse_address.
    It also documents the parameters.
    
    This isn't an attempt to convert the whole file to use bfd_booleans
    more often.  It's simply trying to avoid inconsistencies with new
    SVE parameters.
    
    gas/
    	* config/tc-aarch64.c (parse_address_main): Turn reloc and
    	accept_reg_post_index into bfd_booleans.  Add commentary.
    	(parse_address_reloc): Update accordingly.  Add commentary.
    	(parse_address): Likewise.  Also change accept_reg_post_index
    	into a bfd_boolean here.
    	(parse_operands): Update calls accordingly.
    
    Change-Id: Ia8f585035886401fe282377bb32c4192329896e4