drivers: espi: kconfig: Remove redundant ESPI_PERIPHERAL_CHANNEL deps.

The ESPI_PERIPHERAL_* symbols are surrounded by an
'if ESPI_PERIPHERAL_CHANNEL' in the same file, so no
need to put 'depends on ESPI_PERIPHERAL' on them.

'if' is just a shorthand for 'depends on'.

Also remove a redundant 'if ESPI' from ESPI_XEC.
drivers/espi/Kconfig.xec is sourced within an 'if ESPI' in
drivers/espi/Kconfig.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>