ARM: integrator: Drop unneeded select of SPARSE_IRQ

Support for ARM Ltd. Integrator systems depends on ARCH_MULTIPLATFORM.
As the latter selects SPARSE_IRQ, there is no need for ARCH_INTEGRATOR
to select SPARSE_IRQ.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>