How can I allocate a variable to a specific section?

It could be something more like:

int rawVideo __attribute__ ((section ("onchip_ram_100Kbytes")));

The special .* sections are only created for the main memory that you select for text heap and stack.

Could you show us the begining of your linker script? It is in the Debug/system_description folder of your syslib and is called generated.x

You can also add at the begining of your code this line:

printf("Address of rawVideo is 0x%8.8x\n",&rawVideo);

It will display the variable address and you can check if it has been placed in the correct section.

Why you want this variable there instead of the DDR?