common: console: introduce console_record_isempty helper

Add console_record_isempty to check if console record buffer
contains any data.

Signed-off-by: Ion Agorria <ion@agorria.com>
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20240105072212.6615-4-clamor95@gmail.com


Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>