OMAP4: DPLL cascading: remove unused CM_SHADOW_FREQ_CONFIG2

The value from CM_SHADOW_FREQ_CONFIG2 can't be applied because
GPMC is always active and can't be entered in idle state.

The GPMC is always active because on OMAP4, CPU accesses on
unmapped addresses are redirected to GPMC by L3 interconnect.
CPU is speculative nature and such accesses are possible which
can lead to indirect access to GPMC and if it's clock is
not running, it can result in hang/abort on the platform.
See path d60565948468b for more information.

Change-Id: Ia62d8bf8c59ac3a06445b6f5f9e08ad0c9369c5b
Signed-off-by: Eugen Mandrenko <ievgen.mandrenko@ti.com>