fuzz: Add a linker fuzzer

We add a fuzzer for the linker, that uses RISC-V instruction encoding
logic to create a sequence of valid instructions. Which then is compiled
into a ELF binary and passed to the linker.

Expectation here is that the fuzzer would always generate a valid ELF
binary with valid instructions, and the linker should be able to link it
without any issues.

Currently the ELF binary is limited to one section (.text) and no symbols.
We may want to extend that in the future.

Signed-off-by: Aman <[email protected]>