drivers: serial: dm: Enable DM_FLAG_PRE_RELOC in SBSA pl011 uart driver

drivers: serial: dm: Enable DM_FLAG_PRE_RELOC in SBSA pl011 uart driver

The DM_FLAG_PRE_RELOC shall be enabled in SBSA PL011 uart driver
as this driver is used in NXP based SoCs

It is necessary to have Serial console running before relocation

The !CONFIG_IS_ENABLED(OF_CONTROL) [*] check is set as "workaround"
for DM problem : 4687919684e

This flag is set if board does not support device-tree and using
platform data, In DM Model either of device tree or platform data
can be used to fetch device configuration

It is possible to use SBSA UART with CONFIG_DM_SERIAL but witout
corresponding device tree description (OF_CONTROL)

Other board/SoCs have this flag set unconditionally

Signed-off-by: Vabhav Sharma <vabhav.sharma@nxp.com>