rtlwifi: Create _rtl_dbg_trace function to reduce RT_TRACE code size

This debugging macro can expand to a lot of code.
Make it a function to reduce code size.

(x86-64 defconfig w/ all rtlwifi drivers and allyesconfig)
$ size drivers/net/wireless/realtek/rtlwifi/built-in.o*
   text	   data	    bss	    dec	    hex	filename
 900083	 200499	   1907	1102489	 10d299	drivers/net/wireless/realtek/rtlwifi/built-in.o.defconfig.new
1113597	 200499	   1907	1316003	 1414a3	drivers/net/wireless/realtek/rtlwifi/built-in.o.defconfig.old
1746879	 453503	   8512	2208894	 21b47e	drivers/net/wireless/realtek/rtlwifi/built-in.o.new
2051965	 503311	   8512	2563788	 271ecc	drivers/net/wireless/realtek/rtlwifi/built-in.o.old

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>