Update:

> The PSP2 will most likely be nVidia Tegra 2xx (ARM Cortex-A9 core) driven.
> http://www.semiaccurate.com/2010/07/14/sonys-psp2-powered-nvidias-tegra-line/

ARM Cortex-A9 in the PSP successor ("NGP") has been confirmed by Sony:

http://www.scei.co.jp/corporate/release/110127a_e.html

As the GPU is announced to be the SGX543MP4+ (i.e. non-nVidia) the CPU can't be Tegra, though.