Hi Vinod,
To answer your question on memory protection configurations for external flash (QuadSPI NOR flash), please have my input:
[Vinod] I need to understand, is it possible to implement Memory Protection Unit for external NOR flash
(MX25UW512) IC ?
[Ajesh] Yes, it is possible to protect memory addresses of external flash using XRDC MRC7 configurations. Please refer MRGD register offset for MRC7 configurations for protection of flash addresses.

[Vinod] If NOT, then for implementing MPU which memory do I need to consider other than SRAM
and external NOR ?
[Ajesh] There are protection available using XRDC for all volatile and non-volatile memories using XRDC MRC configuriatons. I have put a snapshot from RM XRDC MRC configuration information below.

[Vinod] If I consider external DRAM in place of NOR Flash IC (MX25UW512), How can I store our application
code in DRAM region and execute from there ? Do I need to do initialization for DRAM during code startup and in Linker file (.ld) I shall map memory section at DRAM address (0x60000000) , will it be ok?
[Ajesh] You can execute your application from any of the memory SRAM/Flash/DRAM, to execute from a specific memory you need to build your application for those addresses by mentioning in linker file with start address.
For DRAM address, as per memory map CM7_0 access DRAM at 0x60000000 and other masters access DRAM at 0x80000000.
Thanks,
Ajesh