thinkpad-acpi: fix incorrect use of TPACPI_BRGHT_MODE_ECNVRAM

HBRV-based default selection of backlight control strategy didn't work
well, at least the X41 defines it but doesn't use it and I don't think
it will stop there.  Switch to a blacklist, and make sure only Radeon-
based models get ECNVRAM.

Symptoms of incorrect backlight mode selection are:

1. Non-working backlight control through sysfs;

2. Backlight gets reset to the lowest level at every shutdown, reboot
   and when thinkpad-acpi gets unloaded;

This fixes a regression in 2.6.30, bugzilla #13826.  This fix is
already present on 2.6.31.

This is a minimal patch for 2.6.30-stable, based on mainline
commits: 050df107,
	 7d95a3d5,
	 59fe4fe3,
	 6da25bf5

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Reported-by: Tobias Diedrich <ranma+kernel@tdiedrich.de>
Reported-by: Robert de Rooy <robert.de.rooy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>