misc: k3_avs: Add OPP_LOW voltage and frequency to vd_data

J7200 SOC supports OPP_LOW and OPP_NOM as two Operating Performance
Points as per (7.5 Operating Performance Points) section in the
Datasheet [0].
- A72SS/MSMC at 2 GHz/1GHz operation must use OPP_NOM.
- A72SS/MSMC at 1 GHz/500 MHz operation can use OPP_NOM or OPP_LOW
  voltage (though OPP_LOW voltage is recommended to reduce power
  consumption).

Add OPP_LOW frequency->voltage entry to vd_data.

The actual OPP voltage for the device is read from the efuse and
updated in k3_avs_probe().
OPP_NOM corresponds to OPP_1 and OPP_LOW to OPP_0 efuse register
fields, as described in the Datasheet [0]
The register offsets and fields are described in the TRM (5.2.6.1.5
WKUP_VTM_VD_OPPVID_j Register) [1].

[0]: https://www.ti.com/lit/gpn/dra821u (J7200 Datasheet)
[1]: https://www.ti.com/lit/pdf/spruiu1 (J7200 TRM)

Signed-off-by: Reid Tonking <reidt@ti.com>
Signed-off-by: Aniket Limaye <a-limaye@ti.com>

drivers/misc/k3_avs.c

@@ -501,6 +501,10 @@ static struct vd_data j721e_vd_data[] = {
 		.dev_id = 202, /* J721E_DEV_A72SS0_CORE0 */
 		.clk_id = 2, /* ARM clock */
 		.opps = {
+			[AM6_OPP_LOW] = {
+				.volt = 0, /* voltage TBD after OPP fuse reading */
+				.freq = 1000000000,
+			},
 			[AM6_OPP_NOM] = {
 				.volt = 880000, /* TBD in DM */
 				.freq = 2000000000,

include/k3-avs.h

@@ -20,6 +20,7 @@
 
 #define NUM_OPPS		4
 
+#define AM6_OPP_LOW		0
 #define AM6_OPP_NOM		1
 #define AM6_OPP_OD		2
 #define AM6_OPP_TURBO		3