misc: atmel_pwm: fix Kconfig symbols

misc: atmel_pwm: fix Kconfig symbols

AT91 symbols AT91SAM9263, AT91SAM9RL, and AT91SAM9G45 do not exist and this
patch changes them to their correct ARCH_* version.
These symbols are chosen instead of the SOC_* ones because this driver is not
converted to DT.
Anyway, the ATMEL_PWM symbol and the associated driver will be removed soon,
during the move to the PWM sub-system.

Reported-by: Paul Bolle <[email protected]>
Acked-by: Alexandre Belloni <[email protected]>
Signed-off-by: Nicolas Ferre <[email protected]>