hw/misc/aspeed_hace: Remove unused code for better readability

hw/misc/aspeed_hace: Remove unused code for better readability

In the previous design of the hash framework, accumulative hashing was not
supported. To work around this limitation, commit 5cd7d85 introduced an
iov_cache array to store all the hash data from firmware.
Once the ASPEED HACE model collected all the data, it passed the iov_cache to
the hash API to calculate the final digest.

However, with commit e3c0752, the hash framework now supports accumulative
hashing. This allows us to refactor the ASPEED HACE model, removing redundant
logic and simplifying the implementation for better readability and
maintainability.

As a result, the iov_count variable is no longer needed—it was previously used
to track how many cached entries were used for hashing.
To maintain VMSTATE compatibility after removing this field, the VMSTATE_VERSION
is bumped to 2

This cleanup follows significant changes in commit 4c1d0af4a28d, making the
model more readable.

- Deleted "iov_cache" and "iov_count" from "AspeedHACEState".
- Removed "reconstruct_iov" function and related logic.
- Simplified "do_hash_operation" by eliminating redundant checks.

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250515081008.583578-2-jamin_lin@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>