As per 'struct mfd_cell ab8500_devs[]' there are not 1, but 3 PWM
devices on the AB8500.  Until now, each of them have referenced
the same Device Tree node.  This change ensures each device has
their own.

Due to recent `dtc` checks [0], nodes cannot share the same node
name, so we are forced to rename the affected nodes by appending
their associated numeric 'bank ID'.

[0] ste-ab8500.dtsi:210.16-214.7: ERROR (duplicate_node_names):
      /soc/prcmu@80157000/ab8500/ab8500-pwm: Duplicate node name
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200622083432.1491715-1-lee.jones@linaro.orgSigned-off-by: Linus Walleij <linus.walleij@linaro.org>