CR-1199552: Fixing mem-bw test for RAVE

[bisingha-xilinx]

Added checks to handle unknown DDR type. Note: Not printing individual bank-name and throughput if the DDR type is unknown

Problem solved by the commit

https://jira.xilinx.com/browse/CR-1199552

Bug / issue (if any) fixed, which PR introduced the bug, how it was discovered

n/a

How problem was solved, alternative solutions (if any) and why they were rejected

Added checks for unknown DDR types

Risks (if any) associated the changes in the commit

n/a

What has been tested and how, request additional testing if necessary

Tested on rave & v70 with known DDR type and unknown DDR type

Documentation impact (if any)

n/a