mtd: denali_spl: do not allocate page_buffer in .bss section

mtd: denali_spl: do not allocate page_buffer in .bss section

Since commit 2580a2a7e719 ("mtd: nand: Increase max sizes of OOB and
Page size"), three boards (ph1_ld4, ph1_pro4, ph1_sld8) fail to build
with the following error message:
  arm-linux-gnueabi-ld.bfd: SPL image plus BSS too big

They compile drivers/mtd/nand/denali_spl.c and it has a page_buffer
as static data:

    static uint8_t page_buffer[NAND_MAX_PAGESIZE];

This buffer required 8KB in .bss section before that commit and now
it has been increased to 16KB.  Given limited code/memory size for SPL,
it is not a good idea to allocate a page buffer statically.  In the
first place, the load address 'dst' can be used as a page buffer.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>