ath10k: fix unsupported chip reset debugs file write

Before this change, after writing "warm_hw_reset" debugfs file, host
will send chip reset command to FW even though FW do not support this
service getting a warning print.

Though there is no FW impact before this change, this patch restricts
chip reset command sent to FW only if FW advertises the support via WMI
service bit.

Removed the redundant check and ath10k_warn() print as well.

New version FW will report chip reset service bit to host. Host allow user
to trigger WLAN chip reset only when fw report this service bit.

For older NON-TLV FW, since it do not report chip reset service bit, host
will not send chip reset command. For older TLV FW, since it report chip
reset service bit, host will send chip reset command.

Tested HW:  QCA9984, WCN3990

QCA9984 FW version: WLAN.BL.3.9.0.2-00042-S-1

Signed-off-by: Yingying Tang <yintang@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>