main/postmarketos-ui-sway: add polkit-elogind dependency

Without the explicit dependency to polkit-elogind the packages polkit and polkit-libs are installed. This however prevents starting sway. Below is the error message from the tinydm log:

00:00:00.028 [ERROR] [wlr] [libseat] [libseat/backend/logind.c:310] Could not activate session: Interactive authentication required.
00:00:00.028 [ERROR] [wlr] [libseat] [libseat/libseat.c:79] No backend was able to open a seat
00:00:00.028 [ERROR] [wlr] [backend/session/session.c:84] Unable to create seat: Function not implemented
00:00:00.028 [ERROR] [wlr] [backend/session/session.c:218] Failed to load session backend
00:00:00.028 [ERROR] [wlr] [backend/backend.c:353] Failed to start a DRM session
00:00:00.028 [ERROR] [sway/server.c:53] Unable to create backend