i965: Fix execution size of scalar TCS barrier setup code.

i965: Fix execution size of scalar TCS barrier setup code.

Previously, the scalar TCS backend was generating:

mov(8)   g17<1>UD     0x00000000UD    { align1 WE_all 1Q compacted };
and(8)   g17.2<1>UD   g0.2<0,1,0>UD   0x0001e000UD  { align1 WE_all 1Q };
shl(8)   g17.2<1>UD   g17.2<8,8,1>UD  0x0000000bUD  { align1 WE_all 1Q };
or(8)    g17.2<1>UD   g17.2<8,8,1>UD  0x00008200UD  { align1 WE_all 1Q };
send(8)  null<1>UW    g17<8,8,1>UD
         gateway (barrier msg) mlen 1 rlen 0 { align1 WE_all 1Q };

This is rubbish - g17.2<8,8,1>UD spans two registers, and is an illegal
region.  Not to mention it clobbers 8 channels of data when we only
wanted to touch m0.2.

Instead, we want:

mov(8)   g17<1>UD     0x00000000UD    { align1 WE_all 1Q compacted };
and(1)   g17.2<1>UD   g0.2<0,1,0>UD   0x0001e000UD  { align1 WE_all };
shl(1)   g17.2<1>UD   g17.2<0,1,0>UD  0x0000000bUD  { align1 WE_all };
or(1)    g17.2<1>UD   g17.2<0,1,0>UD  0x00008200UD  { align1 WE_all };
send(8)  null<1>UW    g17<8,8,1>UD
         gateway (barrier msg) mlen 1 rlen 0 { align1 WE_all 1Q };

Using component() accomplishes this.

Fixes GL44-CTS.tessellation_shader.tessellation_shader_tc_barriers.
barrier_guarded_read_write_calls on Skylake.  Probably fixes other
barrier issues on Gen8+.

v2: Use a group(1, 0) builder so inst->exec_size is set correctly
    (thanks to Francisco Jerez for catching that it was incorrect).

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com> [v1]
Reviewed-by: Francisco Jerez <currojerez@riseup.net>