change location of mt76* firmware, make symlinks

Direct firmware load was failing for my USB WiFI adapter
because kernel tried to load form mediatek/mt76*.,bin

This is also the approach followed for this firmware by other OSes

mt7601.bin

@@ -0,0 +1 @@
+mediatek/mt7601.bin

mt7601u.bin

@@ -0,0 +1 @@
+mediatek/mt7601u.bin

mt7610u.bin

@@ -0,0 +1 @@
+mediatek/mt7610u.bin

mt7662.bin

@@ -0,0 +1 @@
+mediatek/mt7662.bin

mt7662_rom_patch.bin

@@ -0,0 +1 @@
+mediatek/mt7662_rom_patch.bin