[gcn] Add gfx9-generic and generic-associated gfx*

This patch adds gfx9-generic, completing the gfx*-generic support.
It also adds all gfx* devices that are part of any of the gfx*-generic,
i.e. gfx902, gfx904, gfx909, gfx1031, gfx1032, gfx1033, gfx1034,
gfx1035, gfx1101, gfx1102, gfx1150, gfx1151, gfx1152, and gfx1153.

gcc/ChangeLog:

	* config/gcn/gcn-devices.def (GCN_DEVICE): Add gfx9-generic,
	gfx902, gfx904, gfx909, gfx1031, gfx1032, gfx1033, gfx1034,
	gfx1035, gfx1101, gfx1102, gfx1150, gfx1151, gfx1152, and gfx1153.
	Add a currently unused column linking, a specific ISA to a generic
	one (if it exists).
	* config/gcn/gcn-tables.opt: Regenerate
	* doc/invoke.texi (AMD GCN): Add the the new gfc... and the older
	gfx{10-3,11}-generic to -march= as 'experimental'.