mx6qsabrelite: increase the environment offset

The size of the binary created with the default U-boot config is much
greater than the default offset for environment `0x60000`.
In case if that binary is used for booting via MMC it is overlapped with
the environment stored on MMC.
This leads to U-Boot corruption while saving environment with `saveenv`
command and non-bootable SabreLite board.

The offset for environment `CONFIG_ENV_OFFSET=0x60000` was added in
commit a09fea1d but did not count in the change to `0xC0000` if option
`CONFIG_ENV_IS_IN_MMC` is used.

The offset is also used for variant with environment saving onto SPI NOR
flash (with enabled option `CONFIG_ENV_IS_IN_SPI_FLASH`). In that case the
U-Boot binary flashed on SPI NOR is also corrupted after environment
saving with the original 0x60000 offset.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>
Reviewed-by: Tom Rini <trini@konsulko.com>