ot_spi_device: Implement HW registers for TPM mode

[engdoreis]

Implement the hw handled registers
To test use the Opentitan PR lowRISC/opentitan#28697 and run:

bazel test --test_output=streamed --build_tests_only \
    $(bazel query //sw/device/tests:all | grep qemu | grep spi_device) \
    --test_tag_filters="qemu" --override_repository="+qemu+qemu_opentitan=$qemu_repo"

Fix: lowRISC/opentitan#27930

[luismarques]

Any particular reason for the mix of uint32_t and unsigned?

[engdoreis]

Following Emmanuel's advise.

[AlexJones0]

Thanks, this LGTM.

[ziuziakowska]

LGTM, just some minor nits.

[rivos-eblot]

nit: may be capitalize HW & TPM in PR title?

[engdoreis]

The CI failures are related to USB, so I'll merge this PR.