staging: rtlwifi: Improve debugging by using debugfs

The changes in this commit are also being sent to the main rtlwifi
drivers in wireless-next; however, these changes will also be useful for
any debugging of r8822be before it gets moved into the main tree.

Use debugfs to dump register and btcoex status, and also write registers
and h2c.

We create topdir in /sys/kernel/debug/rtlwifi/, and use the MAC address
as subdirectory with several entries to dump mac_reg, bb_reg, rf_reg etc.
An example is
    /sys/kernel/debug/rtlwifi/00-11-22-33-44-55-66/mac_0

This change permits examination of device registers in a dynamic manner,
a feature not available with the current debug mechanism.

We use seq_file to replace RT_TRACE to dump status, then we can use 'cat'
to access btcoex's status through debugfs.
(i.e. /sys/kernel/debug/rtlwifi/00-11-22-33-44-55-66/btcoex)
Other related changes are
1. implement btc_disp_dbg_msg() to access btcoex's common status.
2. remove obsolete field bt_exist
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Yan-Hsuan Chuang <yhchuang@realtek.com>
Cc: Birming Chiu <birming@realtek.com>
Cc: Shaofu <shaofu@realtek.com>
Cc: Steven Ting <steventing@realtek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>