[binutils-gdb] Use i386_target_description to get tdesc_i386

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT ca1fa5eef2912262a0a33875e9a23f2e79a72328 ***

Author: Yao Qi <yao.qi@linaro.org>
Branch: master
Commit: ca1fa5eef2912262a0a33875e9a23f2e79a72328

Use i386_target_description to get tdesc_i386

GDB can call function i386_target_description to get the right target
description rather than tdesc_i386

gdb:

2017-09-04  Yao Qi  <yao.qi@linaro.org>

	* amd64-fbsd-nat.c (amd64fbsd_read_description): Call
	i386_target_description.
	* i386-fbsd-nat.c (i386fbsd_read_description): Call
	i386_target_description.
	* i386-tdep.c (i386_gdbarch_init): Likewise.