hw/i2c: add support for PMBus

QEMU has support for SMBus devices, and PMBus is a more specific
implementation of SMBus. The additions made in this commit makes it easier to
add new PMBus devices to QEMU.

https://pmbus.org/specification-archives/

Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Hao Wu <wuhaotsh@google.com>
Signed-off-by: Titus Rwantare <titusr@google.com>
Message-Id: <20210708172556.1868139-2-titusr@google.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>

hw/arm/Kconfig

@@ -375,6 +375,7 @@ config NPCM7XX
     select ARM_GIC
     select AT24C  # EEPROM
     select PL310  # cache controller
+    select PMBUS
     select SERIAL
     select SSI
     select UNIMP

hw/i2c/Kconfig

@@ -32,3 +32,7 @@ config MPC_I2C
 config PCA954X
     bool
     select I2C
+
+config PMBUS
+    bool
+    select SMBUS

hw/i2c/meson.build

@@ -15,4 +15,5 @@ i2c_ss.add(when: 'CONFIG_VERSATILE_I2C', if_true: files('versatile_i2c.c'))
 i2c_ss.add(when: 'CONFIG_OMAP', if_true: files('omap_i2c.c'))
 i2c_ss.add(when: 'CONFIG_PPC4XX', if_true: files('ppc4xx_i2c.c'))
 i2c_ss.add(when: 'CONFIG_PCA954X', if_true: files('i2c_mux_pca954x.c'))
+i2c_ss.add(when: 'CONFIG_PMBUS', if_true: files('pmbus_device.c'))
 softmmu_ss.add_all(when: 'CONFIG_I2C', if_true: i2c_ss)