drm: bridge: dw-hdmi: Fix the PHY power up sequence

When powering the PHY up we need to wait for the PLL to lock. This is
done by polling the TX_PHY_LOCK bit in the HDMI_PHY_STAT0 register
(interrupt-based wait could be implemented as well but is likely
overkill). The bit is asserted when the PLL locks, but the current code
incorrectly waits for the bit to be deasserted. Fix it, and while at it,
replace the udelay() with a sleep as the code never runs in
non-sleepable context.

To be consistent with the power down implementation move the poll loop
to the power off function.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170305233557.11945-1-laurent.pinchart+renesas@ideasonboard.com