mmc: core: new discard feature support at Samsung eMMC v4.41+.

Support discard feature if MID field in the CID register is 0x15, EXT.CSD[192]
(device version) is 5 and Bit 0 in the EXT.CSD[64] is 1. Also removed REQ_SECURE flag
check to avoid kernel hang.

This patch is released from samsung.

Change-Id: Ibf9c83f3bfee617e58db0d8307da69249797ae8d