Documentation: update debugfs doc for Hisilicon HPRE

Update documentation describing DebugFS for function's QoS limiting.

Signed-off-by: Kai Ye <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

Documentation/ABI/testing/debugfs-hisi-hpre

···
 		has a QM. Select the QM which below qm refers to.
 		Only available for PF.
 
+What:		/sys/kernel/debug/hisi_hpre/<bdf>/alg_qos
+Date:		Jun 2021
+Contact:	[e-mail]
+Description:	The <bdf> is related the function for PF and VF.
+		HPRE driver supports to configure each function's QoS, the driver
+		supports to write <bdf> value to alg_qos in the host. Such as
+		"echo <bdf> value > alg_qos". The qos value is 1~1000, means
+		1/1000~1000/1000 of total QoS. The driver reading alg_qos to
+		get related QoS in the host and VM, Such as "cat alg_qos".
+
 What:		/sys/kernel/debug/hisi_hpre/<bdf>/regs
 Date:		Sep 2019
 Contact:	[e-mail]