Per a suggestion from the hardware team, program the emif_pwr_mgmt_ctrl
and emif_pwr_mgmt_ctrl_shdw registers within the EMIF to hold the
desired delay in cycles that the EMIF waits without an access to enter
self-refresh, in this case 8192 cycles. With this, code desiring to
enter self refresh only has to toggle one bit to enable it.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>