mfd: bcm590xx: Update binding with additional BCM59056 regulators

The BCM59056 supports GPLDO1-6 and VBUS regulators in a secondary
I2C slave address space. Add these regulators to the list of valid
regulator node names for BCM59056.

Signed-off-by: Matt Porter <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/mfd/bcm590xx.txt

···
   The valid regulator node names for BCM59056 are:
   	rfldo, camldo1, camldo2, simldo1, simldo2, sdldo, sdxldo,
 	mmcldo1, mmcldo2, audldo, micldo, usbldo, vibldo,
-	csr, iosr1, iosr2, msr, sdsr1, sdsr2, vsr
+	csr, iosr1, iosr2, msr, sdsr1, sdsr2, vsr,
+	gpldo1, gpldo2, gpldo3, gpldo4, gpldo5, gpldo6,
+	vbus
 
 Example:
 	pmu: bcm59056@8 {