ARM: lpc32xx: remove unused header file mach/irqs.h

The removed LPC32xx mach/irqs.h file is not included in any source
code, function declaration lpc32xx_init_irq() is also unused, remove
them as leftovers after switching to a new interrupt controller
driver.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sylvain Lemieux <slemieux.tyco@gmail.com>