hw/ssi: Rename SSI 'slave' as 'peripheral'

hw/ssi: Rename SSI 'slave' as 'peripheral'

In order to use inclusive terminology, rename SSI 'slave' as
'peripheral', following the specification resolution:
https://www.oshwa.org/a-resolution-to-redefine-spi-signal-names/

Patch created mechanically using:

  $ sed -i s/SSISlave/SSIPeripheral/ $(git grep -l SSISlave)
  $ sed -i s/SSI_SLAVE/SSI_PERIPHERAL/ $(git grep -l SSI_SLAVE)
  $ sed -i s/ssi-slave/ssi-peripheral/ $(git grep -l ssi-slave)
  $ sed -i s/ssi_slave/ssi_peripheral/ $(git grep -l ssi_slave)
  $ sed -i s/ssi_create_slave/ssi_create_peripheral/ \
                                $(git grep -l ssi_create_slave)

Then in VMStateDescription vmstate_ssi_peripheral we restored
the "SSISlave" migration stream name (to avoid breaking migration).

Finally the following files have been manually tweaked:
 - hw/ssi/pl022.c
 - hw/ssi/xilinx_spips.c

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20201012124955.3409127-4-f4bug@amsat.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>