arch/arm/src/lc823450: Fix up_allocate_heap() in lc823450_allocateheap2.c
For lc823450, heap area in flat build mode must start just after
_eronly. Because bss/data area is allocated in lower address than
text area in SRAM. See ld.scripts for details. Also, this change
removes unsed up_allocateheap.c
Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>
Approved-by: GregoryN <gnutt@nuttx.org>