[MIPS] Correct HAL2 Kconfig description

The current HAL2 Kconfig description indicates it is only used on SGI
Indy systems, however all members of the Indigo2 Family have this sound
card as well.  Plus a minor grammatical fix is included.

Signed-off-by: Joshua Kinard <kumba@gentoo.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>