Change default console loglevel during boot up [closed]

Do I need to recompile the kernel,

No.

or is there a way I can get the changed value to be persistent across reboot.

Yes.
Use the kernel command line parameter loglevel:

loglevel=       All Kernel Messages with a loglevel smaller than the
                    console loglevel will be printed to the console. It can
                    also be changed with klogd or other programs. The
                    loglevels are defined as follows:

                    0 (KERN_EMERG)          system is unusable
                    1 (KERN_ALERT)          action must be taken immediately
                    2 (KERN_CRIT)           critical conditions
                    3 (KERN_ERR)            error conditions
                    4 (KERN_WARNING)        warning conditions
                    5 (KERN_NOTICE)         normal but significant condition
                    6 (KERN_INFO)           informational
                    7 (KERN_DEBUG)          debug-level messages

The entire list of parameters possible on the kernel command line are in the Linux/Documentation/kernel-parameters.txt file in the source tree.

Depending on your bootloader (e.g. Grub or U-Boot), you will have to edit text to add this new parameter to the command line. Use cat /proc/cmdline to view the kernel command line used for the previous boot.

Addendum

To display everything, the number supplied for the loglevel parameter would have be be greater than KERN_DEBUG.
That is, you would have to specify loglevel=8.
Or simply use the ignore_loglevel parameter to display all kernel messages.