powerpc/nvram: Enable use Generic NVRAM driver for different size chips

Remove the reliance on a staticly defined NVRAM size, allowing
platforms to support NVRAMs with sizes differing from the standard.

A fall back value is provided for platforms not supporting this extension.

Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/setup_32.c

@@ -210,6 +210,14 @@ void nvram_write_byte(unsigned char val, int addr)
 }
 EXPORT_SYMBOL(nvram_write_byte);
 
+ssize_t nvram_get_size(void)
+{
+	if (ppc_md.nvram_size)
+		return ppc_md.nvram_size();
+	return -1;
+}
+EXPORT_SYMBOL(nvram_get_size);
+
 void nvram_sync(void)
 {
 	if (ppc_md.nvram_sync)