gas: drop TC_ADDRESS_BYTES conditionals

I've been repeatedly confused by, in particular, the .dc.a potable[]
entry being conditional. Grepping in gas/config/ reveals only very few
targets actually #define-ing it. But as of 7be1c4891a the symbol is
always defined, so #ifdef-s are pointless (and, as said, potentially
confusing).

Also adjust documentation to reflect this.

gas/ChangeLog

@@ -1,3 +1,9 @@
+2021-06-14  Jan Beulich  <jbeulich@suse.com>
+
+	* doc/internals.texi (TC_ADDRESS_BYTES): Mention generic default.
+	* read.c (potable, cons_worker): Drop TC_ADDRESS_BYTES
+	conditional.
+
 2021-06-11  H.J. Lu  <hongjiu.lu@intel.com>
 
 	* config/tc-i386.c (x86_cons): Handle GOT/PLT relocations only

gas/doc/internals.texi

@@ -1106,7 +1106,8 @@ You may define this macro to generate a fixup for a data allocation pseudo-op.
 @item TC_ADDRESS_BYTES
 @cindex TC_ADDRESS_BYTES
 Define this macro to specify the number of bytes used to store an address.
-Used to implement @code{dc.a}.  The target must have a reloc for this size.
+Used to implement @code{dc.a}.  If not defined by the target, a default will
+be supplied.  Targets are assumed to have a reloc for this size.
 
 @item TC_INIT_FIX_DATA (@var{fixp})
 @cindex TC_INIT_FIX_DATA

gas/read.c

@@ -364,9 +364,7 @@ static const pseudo_typeS potable[] = {
   {"common.s", s_mri_common, 1},
   {"data", s_data, 0},
   {"dc", cons, 2},
-#ifdef TC_ADDRESS_BYTES
   {"dc.a", cons, 0},
-#endif
   {"dc.b", cons, 1},
   {"dc.d", float_cons, 'd'},
   {"dc.l", cons, 4},
@@ -4095,10 +4093,8 @@ cons_worker (int nbytes,	/* 1=.byte, 2=.word, 4=.long.  */
       return;
     }
 
-#ifdef TC_ADDRESS_BYTES
   if (nbytes == 0)
     nbytes = TC_ADDRESS_BYTES ();
-#endif
 
 #ifdef md_cons_align
   md_cons_align (nbytes);