vmlinux.lds: Add __clkevt_of_table to kernel

The code introduced by commit 0c8893c9095d ("clockevents: Add a
clkevt-of mechanism like clksrc-of") refer to __clkevt_of_table
what doesn't exist in the vmlinux. As a result kernel build
failed with error: "clkevt-probe.c:63: undefined reference to
`__clkevt_of_table’"

Fixes: 0c8893c9095d ("clockevents: Add a clkevt-of mechanism like clksrc-of")
Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>