doc: genrest: Show properties on the correct symbol definition

Previously, symbols defined in multiple locations (e.g.,
Kconfig.defconfig symbols) would incorrectly get all their defaults,
selects, implies, and ranges displayed on the first definition.

This commit uses the Kconfiglib functionality added in 53af8db920066
("kconfiglib: Record which MenuNode has each property") to show such
symbols with all properties in the right location.

The definitions are now listed one-by-one, with the filename/linenr
displayed before each definition. The menu path (e.g.,
'(top menu) -> Device Drivers') is now listed for each definition as
well.

Fixes: #6879

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