m32r: fix build warning

m32r: fix build warning

While building m32r defconfig we got warnings:

  arch/m32r/platforms/m32700ut/setup.c:249:24: warning: 'm32700ut_lcdpld_irq_type' defined but not used [-Wunused-variable]

m32700ut_lcdpld_irq_type is only used when CONFIG_USB is enabled.
Modify the code to declare the related variables and functions only when
CONFIG_USB is enabled.

Link: http://lkml.kernel.org/r/1479244406-7507-1-git-send-email-sudipm.mukherjee@gmail.com
Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>