serial: avoid redundant early UART initialization

serial: avoid redundant early UART initialization

When DEBUG_UART and SKIP_EARLY_DM are enabled, the serial console
is still probed before relocation even though DEBUG_UART already
configures the UART and provides early console output. The debug
UART configuration is sufficient until relocation, making full
serial driver initialization at this stage unnecessary.
Furthermore, the initialization is slow since it runs with dcache
disabled and is repeated again after relocation.

Skip pre-relocation serial probing in this configuration and
defer full UART initialization until after relocation. Update the
GENI UART probe logic accordingly.

This removes redundant UART initialization and improves boot
performance.

Signed-off-by: Aswin Murugan <aswin.murugan@oss.qualcomm.com>