memory: emif: remove unused frequency and voltage notifiers

The driver defined several functions related to handling of frequency
and voltage changes:
 - freq_post_notify_handling
 - freq_pre_notify_handling
 - volt_notify_handling

All these are static, not used inside or outside of driver, and marked
as unused with comment: "TODO: voltage notify handling should be hooked
up to regulator framework as soon as the necessary support is available
in mainline kernel. This function is un-used right now.".

These have been added with commit a93de288 ("memory: emif: handle
frequency and voltage change events") in 2012 and are unused since then.
Additionally mentioned regulator and clock hooking did not happen since
then.  If it did not happen for nine years, let's assume it will not
happen suddenly now.

Remove all unused functions which also allows removal of "t_ck" static
variable "t_ck" and "addressing" member of private structure.

No functionality is lost.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210527154101.80556-1-krzysztof.kozlowski@canonical.com