poplar: fix boot failure caused by serial driver change

poplar: fix boot failure caused by serial driver change

Commit 4687919684e0 ("serial: Remove DM_FLAG_PRE_RELOC flag in various
drivers") essentially drops flag DM_FLAG_PRE_RELOC from serial_pl01x
driver for Poplar platform, because the platform falls into the
following strategy category made by the commit.

  Surround DM_FLAG_PRE_RELOC flag with OF_CONTROL check, for
  drivers that support both statically declared devices and
  configuration from device tree

Before the commit lands, Poplar platform works by statically declaring
pl011 serial device via U_BOOT_DEVICE() with DM_FLAG_PRE_RELOC flag set
in the driver.  But since Poplar also supports device configuration from
device tree, the commit practically drops the flag for Poplar, and hence
breaks the platform from booting.

This patch changes platform code and device tree to initiate pl011
serial device from device tree rather than static declaration, so that
above strategy about DM_FLAG_PRE_RELOC applies to Poplar, and therefore
the reported boot failure gets fixed.

Reported-by: Igor Opaniuk <igor.opaniuk@linaro.org>
Fixes: 4687919684e0 ("serial: Remove DM_FLAG_PRE_RELOC flag in various drivers")
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Igor Opaniuk <igor.opaniuk@linaro.org>
Tested-by: Igor Opaniuk <igor.opaniuk@linaro.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>