Hello Preeti,
A bit complicated to pass multiple values to single property in entity type and URL will not accept 'and' operator for single property if you use filter operation.
technically better option is use get_entityset and add some logic in dpc_ext class to filter strings.
Example:
/sap/opu/odata/sap/TESTQUERY_SRV/TESTQUERY/Results?$filter=ZTCOUNTRY_SSV eq 'ZZ' orZTCOUNTRY_SSV='AA'
if you want use other than get_entityset
Define property type as edm.string and split the string into table and pass those values to you query or RFC.
If you want to use bit complex logic follow the below threads for multiple values for single property.
http://scn.sap.com/thread/3170195