{mimxrt,powerpc,samd}/mpconfigport: Don't override parse chunk alloc.

This was copied from minimal/mpconfigport.h, but it doesn't make sense
for general ports.

Add a comment to minimal/mpconfigport.h to explain why it specifically
overrides it.

This work was funded through GitHub Sponsors.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

ports/mimxrt/mpconfigport.h

@@ -42,7 +42,6 @@ uint32_t trng_random_u32(void);
 #else
 #define MICROPY_GC_STACK_ENTRY_TYPE         uint16_t
 #endif
-#define MICROPY_ALLOC_PARSE_CHUNK_INIT      (32)
 #define MICROPY_ALLOC_PATH_MAX              (256)
 
 // MicroPython emitters

ports/minimal/mpconfigport.h

@@ -17,6 +17,8 @@
 #define MICROPY_ENABLE_EXTERNAL_IMPORT    (1)
 
 #define MICROPY_ALLOC_PATH_MAX            (256)
+
+// Use the minimum headroom in the chunk allocator for parse nodes.
 #define MICROPY_ALLOC_PARSE_CHUNK_INIT    (16)
 
 // type definitions for the specific machine

ports/powerpc/mpconfigport.h

@@ -38,7 +38,6 @@
 #define MICROPY_QSTR_BYTES_IN_HASH  (1)
 #define MICROPY_QSTR_EXTRA_POOL     mp_qstr_frozen_const_pool
 #define MICROPY_ALLOC_PATH_MAX      (256)
-#define MICROPY_ALLOC_PARSE_CHUNK_INIT (16)
 #define MICROPY_EMIT_X64            (0)
 #define MICROPY_EMIT_THUMB          (0)
 #define MICROPY_EMIT_INLINE_THUMB   (0)

ports/samd/mpconfigport.h

@@ -34,7 +34,6 @@
 // Memory allocation policies
 #define MICROPY_GC_STACK_ENTRY_TYPE         uint16_t
 #define MICROPY_GC_ALLOC_THRESHOLD          (0)
-#define MICROPY_ALLOC_PARSE_CHUNK_INIT      (32)
 #define MICROPY_ALLOC_PATH_MAX              (256)
 #define MICROPY_QSTR_BYTES_IN_HASH          (1)