[ARM] locomo: remove unused IRQs and avoid unnecessary cascade

IRQ_LOCOMO_* are never used elsewhere, remove these definitions. As well
as the cascade of these IRQs. IRQ_LOCOMO_*_BASE changed to IRQ_LOCOMO_*.

IRQ_LOCOMO_LT and IRQ_LOCOMO_SPI are likely to be used in a same way as
IRQ_LOCOMO_KEY.

IRQ_LOCOMO_GPIO and the demultiplex handler should really be living
somewhere else.

Signed-off-by: Eric Miao <eric.y.miao@gmail.com>