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CY62157ESL has a wide voltage range: 2.2V - 3.6V and 4.5V - 5.5V. If you are operating the device in 2.2V - 3.6V range and powering up the SRAM through a battery when the power is down, you need to connect Only chip enable(CE) and byte enables (BHE and BLE) need to be tied to CMOS levels to meet the ISB2 / ICCDR spec. Other inputs can be left floating.
Let me know if you need any further help.
I will drive CE_N to VCC and use the 60K resistors to pull BHE_N and BLE_N to VSS (GND). I believe the load on the other pins will look like a diode to GND. I assume this is OK if leaving them floating is OK.
Use of supervisory chips is what Cypress recommends. Having pull up/ pull down resistors is ok but not recommended. I am attaching an app note below which is aimed at addressing exact same issue that is bothering you. Have a look and then let me know if you have any more doubts.