onenand: Fix compile errors due to FlexOneNAND

This patch fixes the compile error while trying to
compile for omap3evm.

env_onenand.c: In function 'env_relocate_spec':
env_onenand.c:70: error: 'CONFIG_ENV_ADDR_FLEX' undeclared
 (first use in this function)
env_onenand.c:70: error: (Each undeclared identifier is re
ported only once
env_onenand.c:70: error: for each function it appears in.)
env_onenand.c: In function 'saveenv':
env_onenand.c:106: error: 'CONFIG_ENV_ADDR_FLEX' undeclare
d (first use in this function)
env_onenand.c:107: error: 'CONFIG_ENV_SIZE_FLEX' undeclare
d (first use in this function)

Signed-off-by: Sanjeev Premi <premi@ti.com>
Acked-by: Tom Rix <Tom.Rix@windriver.com>