scsi: ufs: Remove pre-defined initial voltage values of device power

UFS specficication allows different VCC configurations for UFS devices,
for example:

	(1). 2.70V - 3.60V (Activated by default in UFS core driver)
	(2). 1.70V - 1.95V (Activated if "vcc-supply-1p8" is declared in
                          device tree)
	(3). 2.40V - 2.70V (Supported since UFS 3.x)

With the introduction of UFS 3.x products, an issue is happening that UFS
driver will use wrong "min_uV-max_uV" values to configure the voltage of
VCC regulator on UFU 3.x products with the configuration (3) used.

To solve this issue, we simply remove pre-defined initial VCC voltage
values in UFS core driver with below reasons,

1. UFS specifications do not define how to detect the VCC configuration
   supported by attached device.

2. Device tree already supports standard regulator properties.

Therefore VCC voltage shall be defined correctly in device tree, and shall
not changed by UFS driver. What UFS driver needs to do is simply enable or
disable the VCC regulator only.

Similar change is applied to VCCQ and VCCQ2 as well.

Note that we keep struct ufs_vreg unchanged. This allows vendors to
configure proper min_uV and max_uV of any regulators to make
regulator_set_voltage() works during regulator toggling flow in the
future. Without specific vendor configurations, min_uV and max_uV will be
NULL by default and UFS core driver will enable or disable the regulator
only without adjusting its voltage.

Link: https://lore.kernel.org/r/20201202091819.22363-1-stanley.chu@mediatek.com
Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Can Guo <cang@codeaurora.org>
Acked-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>