loader: riscv: Initial support

[endeneer]

Initial porting to support loading Linux PE Image and dtb on RISC-V platform.

Summary of the PR

Hi @roypat, as mentioned in rust-vmm/kvm-bindings#92 (comment), here is the commit porting linux-loader to RISC-V.

Test result

running 20 tests
test cmdline::tests::test_error_try_from ... ok$<2>
test cmdline::tests::test_add_virtio_mmio_device ... ok$<2>
test cmdline::tests::test_as_cstring ... ok$<2>
test cmdline::tests::test_insert_emoji ... ok$<2>
test cmdline::tests::test_insert_equals ... ok$<2>
test cmdline::tests::test_insert_hello_world ... ok$<2>
test cmdline::tests::test_insert_multi ... ok$<2>
test cmdline::tests::test_insert_space ... ok$<2>
test cmdline::tests::test_insert_string ... ok$<2>
test cmdline::tests::test_insert_kv ... ok$<2>
test cmdline::tests::test_partial_eq ... ok$<2>
test cmdline::tests::test_try_from_cmdline_for_vec ... ok$<2>
test cmdline::tests::test_try_from ... ok$<2>
test cmdline::tests::test_insert_too_large ... ok$<2>
test configurator::tests::test_error_messages ... ok$<2>
test configurator::tests::test_bootparam_list_addition ... ok$<2>
test configurator::tests::test_bootparams ... ok$<2>
test loader::tests::test_cmdline_overflow ... ok$<2>
test loader::riscv::pe::tests::load_image ... ok$<2>
test loader::tests::test_cmdline_write_end_regresion ... ok$<2>

test result: ok$<2>. 20 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.09s

Requirements

Before submitting your PR, please make sure you addressed the following
requirements:

• All commits in this PR are signed (with git commit -s), and the commit
  message has max 60 characters for the summary and max 75 characters for each
  description line.
• All added/changed functionality has a corresponding unit/integration
  test.
• [N/A] All added/changed public-facing functionality has entries in the "Upcoming
  Release" section of CHANGELOG.md (if no such section exists, please create one).
• Any newly added unsafe code is properly documented.

[rbradford]

Thanks for looking at this!

[endeneer]

Update:

• Rebased with latest main branch.
• Use read_exact_volatile_from instead of read_exact_from as in the commit build: update vm-memory requirement from 0.12.2 to 0.13.0.