soc: imx: gpcv2: move reset assert after requesting domain power up

The i.MX8MM VPU power up sequence is a bit special, it must follow:
1. request power up
2. reset assert
3. reset deassert

This change in this patch will not affect other domains, because
the power domain default is in asserted state, unless bootloader
deassert the reset. It also applies to GPU power domain.

Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>