kernel: Convert formatter strings to use PRI defines

To allow for various libc implementations (like newlib) in which the way
various {u}int{8,16,32}_t types are defined vary between both libc
implementations and across architectures we need to utilize the PRI
defines.

Change-Id: Ie884fb67015502288152ecbd64c37961a4f538e4
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>