Make GOT entry size target-dependent

Make GOT entry size target-dependent

The GOT entry size is target-dependent.  This patch adds a got_entry_size
function to Sized_target class so that a target can provide a value
different from default.

	PR gold/19184
	* incremental.cc (Got_plt_view_info): Add got_entry_size.
	(Local_got_offset_visitor::visit): Replace got_entry_size_
	with info_.got_entry_size.
	(Local_got_offset_visitor::got_entry_size_): Removed.
	(Global_got_offset_visitor::visit): Replace got_entry_size_
	with info_.got_entry_size.
	(Global_got_offset_visitor::got_entry_size_): Removed.
	(Output_section_incremental_inputs::write_got_plt): Initialize
	view_info.got_entry_size.
	* target.h (Sized_target::got_entry_size): New virtual function.
	* x86_64.cc (Target_x86_64::got_entry_size): New function.