ARM: 7019/1: Footbridge: select CLKEVT_I8253 for ARCH_NETWINDER

Since commit 8560a6cf
"arm: Footbridge: Use common i8253 clockevent",
ARCH_NETWINDER needs to select CLKEVT_I8253.

This patch fixes below build error with "make netwinder_defconfig".

  LD      .tmp_vmlinux1
arch/arm/mach-footbridge/built-in.o: In function `isa_timer_init':
isa-rtc.c:(.init.text+0x12c8): undefined reference to `clockevent_i8253_init'
isa-rtc.c:(.init.text+0x12d0): undefined reference to `i8253_clockevent'
arch/arm/mach-footbridge/built-in.o:(.data+0x198): undefined reference to `i8253_clockevent'
make: *** [.tmp_vmlinux1] Error 1

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>