mmc: pwrseq-simple: Add an optional post-power-on-delay

  See ../clocks/clock-bindings.txt for details.

- clock-names : Must include the following entry:

  "ext_clock" (External clock provided to the card).

- post-power-on-delay-ms : Delay in ms after powering the card and

	de-asserting the reset-gpios (if any)

Example:

#include <linux/device.h>

#include <linux/err.h>

#include <linux/gpio/consumer.h>

#include <linux/delay.h>

#include <linux/property.h>

#include <linux/mmc/host.h>

struct mmc_pwrseq_simple {

	struct mmc_pwrseq pwrseq;

	bool clk_enabled;

	u32 post_power_on_delay_ms;

	struct clk *ext_clk;

	struct gpio_descs *reset_gpios;

};

	struct mmc_pwrseq_simple *pwrseq = to_pwrseq_simple(host->pwrseq);

	mmc_pwrseq_simple_set_gpios_value(pwrseq, 0);

	if (pwrseq->post_power_on_delay_ms)

		msleep(pwrseq->post_power_on_delay_ms);

}

static void mmc_pwrseq_simple_power_off(struct mmc_host *host)

		return PTR_ERR(pwrseq->reset_gpios);

	}

	device_property_read_u32(dev, "post-power-on-delay-ms",

				 &pwrseq->post_power_on_delay_ms);

	pwrseq->pwrseq.dev = dev;

	pwrseq->pwrseq.ops = &mmc_pwrseq_simple_ops;

	pwrseq->pwrseq.owner = THIS_MODULE;