drm/amdkfd: Align partition memory size to page size

The compute partition memory size calculated from KFD_XCP_MEMORY_SIZE
may not align to page size if xcp_mgr->num_xcp_per_mem_partition is 6.

Change the KFD_XCP_MEMORY_SIZE macro to return page align size, so KFD
node memory size reported in sysfs is page align size, to avoid
application VRAM allocation failure because application may use the size
directly and Thunk requires the memory allocation size is page size
align.

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>