ARM: bcm2835: defconfig updates

Now that we have an SDHCI driver, enable the block layer, and common
filesystems; MSDOS for the SoC-required firmware partition, and ext2,
ext3, ext4 for a root partition.

Enable GPIO_SYSFS to allow GPIO twiddling from user-space; likely a
common activity on this hardware.

Other non-semantic diffs due to rebuilding defconfig using the latest
Kconfig defaults etc.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>