xtensa: split bootparam and kernel meminfo

Bootparam meminfo is a bootloader ABI, kernel meminfo is for the kernel
bookkeeping, keep them separate. Kernel doesn't care of memory region
types, so drop the type field and don't pass it to add_sysmem_bank.
Move kernel sysmem structures and prototypes to asm/sysmem.h and sysmem
variable and add_sysmem_bank to mm/init.c

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>