amdgcn: config.gcc - enable gfx1030 and gfx1100 multilib; add them to the docs

amdgcn: config.gcc - enable gfx1030 and gfx1100 multilib; add them to the docs

gcc/ChangeLog:

	* config.gcc (amdgcn-*-*): Add gfx1030 and gfx1100 to
	TM_MULTILIB_CONFIG.
	* doc/install.texi (Configuration amdgcn-*-*): Mention gfx1030/gfx1100.
	* doc/invoke.texi (AMD GCN Options): Add gfx1030 and gfx1100 to
	-march/-mtune.

libgomp/ChangeLog:

	* testsuite/libgomp.c/declare-variant-4.h: Add variant functions
	for gfx1030 and gfx1100.
	* testsuite/libgomp.c/declare-variant-4-gfx1030.c: New test.
	* testsuite/libgomp.c/declare-variant-4-gfx1100.c: New test.

Signed-off-by: Tobias Burnus <tburnus@baylibre.com>