drm/vc4: hvs: Change prototype of __vc4_hvs_alloc to pass registers

The BCM2712 HVS has registers to report the size of the various SRAM the
driver uses, and their size actually differ depending on the stepping.

The initialisation of the memory pools happen in the __vc4_hvs_alloc()
function that also allocates the main HVS structure, that will then hold
the pointer to the memory mapping of the registers.

This creates some kind of circular dependency that we can break by
passing the mapping pointer as an argument for __vc4_hvs_alloc() to use
to query to get the SRAM sizes and initialise the memory pools
accordingly.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>