Documentation: power: Correct a mistaken configuration option

Somehow CONFIG_PSTORE_FIRMWARE ended up in this document when I intended
it to be CONFIG_CHROMEOS_PSTORE. Correct the configuration option and
make it clear that not all options are required.

Fixes: b1f02f005a2e ("Documentation: power: Add document on debugging shutdown hangs")
Reported-by: Rodrigo Siqueira <[e-mail]>
Signed-off-by: Mario Limonciello (AMD) <[e-mail]>
[ rjw: Fixes: tag ]
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/power/shutdown-debugging.rst

···
 * ``CONFIG_PSTORE_CONSOLE=y``
 
 Additionally, enable a backend to store the data. Depending upon your platform
-some options include:
+some potential options include:
 
 * ``CONFIG_EFI_VARS_PSTORE=y``
 * ``CONFIG_PSTORE_RAM=y``
-* ``CONFIG_PSTORE_FIRMWARE=y``
+* ``CONFIG_CHROMEOS_PSTORE=y``
 * ``CONFIG_PSTORE_BLK=y``
 
 Kernel Command-line Parameters