target: simplify register get/set ops

No need to indirect from registered integers to pointers.
Just stash the pointers directly in the register struct,
and don't even bother registering.

This is a small code shrink, speeds register access just
a smidgeon, and gets rid of another rude exit() path.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/target/armv7a.c

@@ -157,7 +157,6 @@ struct reg armv7a_gdb_dummy_fp_reg =
 	.valid = 1,
 	.size = 96,
 	.arch_info = NULL,
-	.arch_type = 0,
 };
 
 void armv7a_show_fault_registers(struct target *target)