scsi: docs: Organize the SCSI documentation

Break the SCSI documentation up into categories:

Introduction, APIs, driver parameters, and host adapter drivers instead
of alphabetical by document file name (i.e., no organization).

Signed-off-by: Randy Dunlap <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Cc: "James E.J. Bottomley" <[e-mail]>
Cc: "Martin K. Petersen" <[e-mail]>
Cc: [e-mail]
Cc: Jonathan Corbet <[e-mail]>
Cc: [e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

Documentation/scsi/index.rst

···
 .. toctree::
    :maxdepth: 1
 
+Introduction
+============
+
+.. toctree::
+   :maxdepth: 1
+
+   scsi
+
+SCSI driver APIs
+================
+
+.. toctree::
+   :maxdepth: 1
+
+   scsi_mid_low_api
+   scsi_eh
+
+SCSI driver parameters
+======================
+
+.. toctree::
+   :maxdepth: 1
+
+   scsi-parameters
+   link_power_management_policy
+
+SCSI host adapter drivers
+=========================
+
+.. toctree::
+   :maxdepth: 1
+
    53c700
    aacraid
    advansys
···
    hpsa
    hptiop
    libsas
-   link_power_management_policy
    lpfc
    megaraid
    ncr53c8xx
···
    ppa
    qlogicfas
    scsi-changer
-   scsi_eh
    scsi_fc_transport
    scsi-generic
-   scsi_mid_low_api
-   scsi-parameters
-   scsi
    sd-parameters
    smartpqi
    st