elf: fix cache flushing in 'bootelf -p' command

Currently there are two problems in 'bootelf -p' (load elf by segments)
command:
- bss section is not flushed, so booted elf can have non zero values
  in bss;
- at least on ARM there are 'CACHE: Misaligned operation at
  range...' warnings

Use p_memsz instead of p_filesz during cache flushing for elf segment.
p_filesz doesn't include zero initialized memory (e.g. bss section),
which also should be flushed.

Align these cache flushes to line boundaries.

Signed-off-by: Kurban Mallachiev <mallachiev@ispras.ru>
diff --git a/cmd/elf.c b/cmd/elf.c
index 7bad1f8..d883be4 100644
--- a/cmd/elf.c
+++ b/cmd/elf.c
@@ -53,7 +53,8 @@
 		if (phdr->p_filesz != phdr->p_memsz)
 			memset(dst + phdr->p_filesz, 0x00,
 			       phdr->p_memsz - phdr->p_filesz);
-		flush_cache((unsigned long)dst, phdr->p_filesz);
+		flush_cache(rounddown((unsigned long)dst, ARCH_DMA_MINALIGN),
+			    roundup(phdr->p_memsz, ARCH_DMA_MINALIGN));
 		++phdr;
 	}
 
@@ -167,7 +168,8 @@
 		if (phdr->p_filesz != phdr->p_memsz)
 			memset(dst + phdr->p_filesz, 0x00,
 			       phdr->p_memsz - phdr->p_filesz);
-		flush_cache((unsigned long)dst, phdr->p_filesz);
+		flush_cache(rounddown((unsigned long)dst, ARCH_DMA_MINALIGN),
+			    roundup(phdr->p_memsz, ARCH_DMA_MINALIGN));
 		++phdr;
 	}