omap5-board-common: remove not physically existing vdds_1v8_main fixed-regulator

This device tree include file describes a fixed-regulator
connecting smps7_reg output (1.8V) to some 1.8V rail and
consumers (vdds_1v8_main).

This regulator does not physically exist.

I assume it was introduced as a wrapper around smps7_reg
to provide a speaking signal name "vdds_1v8_main" as label.

This fixed-regulator without real function was not an issue
in driver code until

  Commit 98e48cd9 ("regulator: core: resolve supply for boot-on/always-on regulators")

introduced a new check for regulator initialization which
makes Palmas regulator registration fail:

[    5.407712] ldo1: supplied by vsys_cobra
[    5.412748] ldo2: supplied by vsys_cobra
[    5.417603] palmas-pmic 48070000.i2c:palmas@48:palmas_pmic: failed to register 48070000.i2c:palmas@48:palmas_pmic regulator

The reason is that the supply-chain of regulators is too
long and goes from ldo3 through the virtual vdds_1v8_main
regulator and then back to smps7. This adds a cross-dependency
of probing Palmas regulators and the fixed-regulator which
leads to probe deferral by the new check and is no longer
resolved.

Since we do not control what device tree files including this
one reference (either &vdds_1v8_main or &smps7_reg or both)
we keep both labels for smps7 for compatibility.

Fixes: 98e48cd9 ("regulator: core: resolve supply for boot-on/always-on regulators")
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>