ARM: OMAP3: clock data: Add missing enable/disable for EMU clock

The ETM/ETB drivers for OMAP3, enable the emu_src_ck clock in order
to access the ETM/ETB hardware. The emu_src_ck should enable the EMU
clock domain so that the ETM/ETB hardware is accessible. However,
currently when enabling the emu_src_ck the EMU clock domain is not
being enabled and so the ETM/ETB drivers are failing. Add enable/disable
clock functions to enable the EMU clock domain when enabling the
emu_src_ck.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>