rtlwifi: rtl8723be: Make functions static & rm sw.h

Some of functions which were exposed in sw.h, are only used in sw.c, so
just make them static. This makes sw.h unnecessary, so remove it.

Signed-off-by: Amadeusz Sławiński <amade@asmblr.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>