place_phys cannot allocate across platform memory region boundaries and fails silently

[DavidMCerdeira]

Describe the bug

Physical memory allocations requested via the .place_phys memory attribute cannot span across platform-defined memory region boundaries.
When an allocation request overlaps the boundary between two mem_region entries, the allocation fails without error, warning, or diagnostic output, leaving the caller unaware of the failure.

For example, on the Raspberry Pi 4 the platform description may define two memory regions:

.cpu_num = 4,
.region_num = (RPI4_MEM_GB > 1) ? 2 : 1,
.regions = (struct mem_region[]) {
    {
        .base = 0x80000,
        .size = 0x40000000 - 0x80000 - 0x4c00000,
    },
    {
        .base = 0x40000000,
        .size = ((RPI4_MEM_GB - 1) * 0x40000000ULL) - 0x4000000,
    },
},

If a .place_phys allocation request covers the 0x40000000 boundary (e.g., a region that begins below 0x40000000 and extends past it), the allocation:

• does not occur for the portion over the first memory region
• does not report any error to the user

Expected behavior

• Allocations that span multiple mem_region entries should either:

  • be correctly split/handled internally, or
  • be explicitly rejected with a clear error message

• Silent failures should be replaced with proper diagnostics or error returns

Impact

• Debugging becomes extremely difficult due to lack of feedback
• Platform descriptions using disjoint memory regions (e.g., >1GB RPI4 configurations) silently break valid physical placement requests

Steps to reproduce

1. Use a platform description that defines multiple memory regions (such as RPI4 with >1GB)
2. Request a .place_phys allocation whose range crosses a mem_region boundary
3. Observe that memory over the first memory region range is not allocated and no error is reported

Proposed fix / suggestions

At minimum, the system should:

• Detect allocations that cross region boundaries

• Emit an error such as:

  ERROR: place_phys allocation spans multiple platform memory regions, which is not supported.
         Requested range: 0xXXXXXXXX – 0xXXXXXXXX
         Platform regions:
           [0] 0xXXXXXXXX – 0xXXXXXXXX
           [1] 0xXXXXXXXX – 0xXXXXXXXX
  

• Or implement support for splitting physical allocations accordingly

[josecm]

Should we just start by adding the check as a fix? Then proceed to handle the cross (contiguous!) regions allocation and physical placement?