libqos/ahci: add ahci command functions

This patch adds the AHCICommand structure, and a set of functions to
operate on the structure.

ahci_command_create - Initialize and create a new AHCICommand in memory
ahci_command_free - Destroy this object.
ahci_command_set_buffer - Set where the guest memory DMA buffer is.
ahci_command_commit - Write this command to the AHCI HBA.
ahci_command_issue - Issue the committed command synchronously.
ahci_command_issue_async - Issue the committed command asynchronously.
ahci_command_wait - Wait for an asynchronous command to finish.
ahci_command_slot - Get the number of the command slot we committed to.

Helpers:
size_to_prdtl       - Calculate the required minimum PRDTL size from
                      a buffer size.
ahci_command_find   - Given an ATA command mnemonic, look it up in the
                      properties table to obtain info about the command.
command_header_init - Initialize the command header with sane values.
command_table_init  - Initialize the command table with sane values.

[Peter Maydell <peter.maydell@linaro.org> reported the following clang
warning:

  tests/libqos/ahci.c:598:3: warning: redefinition
  of typedef 'AHCICommand' is a C11 feature
      [-Wtypedef-redefinition]
  } AHCICommand;

I have replaced typedef struct ... AHCICommand; with struct ... ;
--Stefan]

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 1423158090-25580-13-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
