log: correct and check array size of log categories

The log command has led to NULL dereferences if an unknown category name
name was used due to missing entries in the list of category names.

Add compile time checks for the array sizes of log_cat_name and
log_lvl_name to avoid future mishaps.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>