ALSA: atmel: fix building the ac97 driver for at91-multiplatform

ALSA: atmel: fix building the ac97 driver for at91-multiplatform

at91 will no longer export the mach/cpu.h and mach/hardware.h header files
in the future, which would break building the atmel ac97c driver.

Since the cpu_is_* check is only used to find out whether we are running
on avr32 or arm/at91, we can hardcode that check in the ARM case.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: http://www.spinics.net/lists/arm-kernel/msg382068.html
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>