arm: mvebu: maxbcm: Fix compilation warning and add Spansion SPI NOR support

This patch fixes the following compilation warning for maxbcm:

Building maxbcm board...
   text    data     bss     dec     hex filename
 160075    6596   38240  204911   3206f ./u-boot
board/maxbcm/maxbcm.c: In function 'reset_phy':
board/maxbcm/maxbcm.c:68:6: warning: unused variable 'reg' [-Wunused-variable]
  u16 reg;
      ^
board/maxbcm/maxbcm.c:66:6: warning: unused variable 'devadr' [-Wunused-variable]
  u16 devadr = CONFIG_PHY_BASE_ADDR;
      ^

Additionally support Spansion SPI NOR flash is added. With larger SPI device
support via the CONFIG_SPI_FLASH_BAR define.

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Luka Perkov <luka.perkov@sartura.hr>