soc/intel_adsp: Unify HP-SRAM definition

The HP SRAM block address and size is specified in four different ways
(devicetree, "SRAM_*", "HP_SRAM_*" and "L2_SRAM_*" macros).  Unify,
moving the C definition (which just fetches it from dts) to a single
header and out of the platform layer.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>